DESCRIPTION OF THE APPENDAGES OF INDIVIDUAL SPECIMENS.
Triarthrus becki Green.
In order to make easily available the evidence on which the present
knowledge of the appendages of Triarthrus and _Cryptolithus_ rests, it
has seemed wise to publish brief descriptions and photographic figures
of some of the better specimens preserved in the Yale University
Museum. These specimens are pyritic replacements, and while they do
not as yet show any signs of decomposition, it should be realized that
it is only a matter of time when either they will be self-destroyed
through oxidation, or else embedded for safe keeping in such a fashion
that they will not be readily available for study. It is therefore
essential to keep a photographic record of the more important
individuals.
Specimen No. 220 (pl. 3, fig. 2).
Illustrated: Amer. Geol., vol. 15, 1895, pl. 4 (drawing);
Amer. Jour. Sci., vol. 13, 1902, pl. 3 (photograph).
This is one of the largest specimens showing appendages, and is
developed from the ventral side. It shows some appendages on all parts
of the body, but its special features are the exhibition of the shafts
on the proximal ends of the antennules, the rather well preserved
appendages of the cephalon and anterior part of the thorax, and the
preservation of the anal opening. In the drawing in the American
Geologist, the right and left sides are reversed as in a mirror, a
point which should be borne in mind when comparing that figure with
a photograph or description.
The shaft of the left antennule is best preserved and is short,
cylindrical, somewhat enlarged and ball-shaped at the proximal end. It
is 1.5 mm. long. The posterior part of the hypostoma is present, but
crushed, and the metastoma is not visible, the pieces so indicated
in Beecher's figure being the rim of the hypostoma. Back of the
hypostoma may be seen four (not three as in Beecher's figure) pairs
of gnathites, the first three pairs broad and greatly overlapping, the
fourth pair more slender, but poorly preserved. The inner edges of the
gnathites on the right side are distinctly nodulose, and roughened for
mastication.
The outer ends of one endopodite and three exopodites project beyond
the margin on the right side. The dactylopodite of the endopodite is
especially well preserved. It is cylindrical, the end rounded but not
enlarged or pointed, and bears three small sharp spines, all in a
horizontal plane, one anterior, one central, and one posterior. The
outer ends of the exopodites show about ten segments each (in 2.5 mm.)
beyond the margin of the test, and from three to five setæ attached to
the posterior side of each segment. These hairs are attached in a
groove, well shown in this specimen. On the anterior margin of the
exopodite there is a minute spine at each joint.
_Measurements:_ Length, 38 mm.; width at back of cephalon, 19 mm.
Specimen No. 210 (pl. 2, fig. 3).
Illustrated: Amer. Jour. Sci., vol. 46, 1893, p. 469, fig. 1
(head and right side); Amer. Geol., vol. 13, 1894, pl. 3, fig. 7
(same figure as the last); Amer. Jour. Sci., vol. 13, 1902, pl. 2,
fig. 1 (photograph).
This individual supplied the main basis for Professor Beecher's first
figure showing the appendages of the thorax, the head and appendages
of the right side having been taken from it, and the appendages of
the left side from No. 206. Such of the endopodites as are well
preserved show from three to four segments projecting beyond the test,
and the dactylopodites have one or two terminal spines. The antennules
are unusually well preserved and have about forty segments each in
front of the cephalon, or an average of five to one millimeter.
Specimens 209 and 210 are on a slab about 7 × 5.5 inches, and with
them are twelve other more or less well preserved individuals, all but
one of which are smaller than these. Two of the fourteen are ventral
side up on the slab, which means dorsal side up in the rock. Nine are
oriented in one direction, two at exactly right angles to this, and
three at an angle of 45 with the others. If the majority of the
specimens are considered to be headed northward, then seven are so
oriented, two northeast, one east, two south, one southwest, and one
west.
Nine of the specimens show antennules. Five of these are specimens
headed north, and in all of them the antennules are in or very near
the normal position. The antennules of two, one headed east and the
other west, are imperfectly preserved, but the parts remaining diverge
much more than do the antennules of those in the normal position. The
individual headed southwest has one antennule broken off, while the
other is curved back so that its tip is directed northward. Another
one, headed south, has the antennules in the normal position. These
observations indicate that the specimens were oriented by currents of
water, rather than in life attitudes, and that the distal portions of
the antennules were relatively flexible.
_Measurements:_ The specimen (No. 210) is 20 mm. long, 9.5 mm. wide at
the back of the cephalon, and the antennules project 8 mm. in front of
the head. The smallest specimen on the slab is 6.5 mm. long. A
specimen 7.5 mm. long has antennules which project 2.5 mm. in front of
the cephalon.
Specimen No. 201 (pl. 2, fig. 1; pl. 3, fig. 4).
Illustrated: Amer. Jour. Sci., vol. 46, 1893, p. 469, figs. 2, 3;
Amer. Geol., vol. 13, 1894, pl. 3, figs. 8, 9.
An entire specimen 17 mm. long, exposed from the dorsal side. It shows
only traces of the appendages of the head, but displays well those of
the anterior part of the thorax, and a number of appendages emerge
from under the abdominal shield. This specimen is of particular
interest as it is the subject of the first of Professor Beecher's
papers on appendages of trilobites. On the right side the pleura have
been removed, so as to expose the appendages of the second, third, and
fourth segments from above. The first two of the appendages on the
right are best preserved, and these are the ones figured. They belong
to the second and third segments. The endopodites of each are ahead of
the exopodites, and the proximal portion of each exopodite overlies
portions of the first two segments (second and third) of the
corresponding endopodite. The coxopodites are not visible, but very
nearly the full length of the first segment of the endopodite (the
basipodite) is exposed. The first two visible segments (the first and
second) extend just to the margin of the pleural lobe, while the other
four extend beyond the dorsal cover. The segments decrease in length
outward, but not regularly, the meropodite being generally longer than
the ischiopodite or the carpopodite. The terminal segment
(dactylopodite) is short and bears short sharp hair-like spines which
articulate in sockets at the distal end. On this specimen the anterior
limb on the right side shows one terminal spine, the second endopodite
on that side has two, and two of the endopodites on the left-hand side
preserve two each. The segments of the limbs are nearly cylindrical,
but the ischiopodites and meropodites of several of the endopodites
show rather deep longitudinal grooves which appear to be rather the
result of the shrinkage of the thin test than natural conformations.
The endopodites on the left-hand side have a number of short, sharp,
movable, hair-like spines, and cup-shaped depressions which are the
points of insertion of others. On the distal end of the carpopodite of
the first thoracic segment there seems to have been a spine, whose
place is now shown by a pit. This same endopodite shows, rather
indistinctly, three pits in the groove of the carpopodite, and the
propodite has two. On the endopodite of the second appendage on this
side, both the carpopodite and propodite possess a fine hair-like
articulated spine at the distal end, that of the propodite arising on
the dorsal and that of the carpopodite on the posterior side. On the
dorsal side of the carpopodite there are three pits for the
articulation of spines, and on the propodite, one.
The exopodites belonging to the thoracic segments are of equal length
with the endopodites, and while the proximal portion of each is
stouter than that of the corresponding endopodite, the exopodites
taper to a hair-like termination, while the endopodites remain fairly
stout to the distal segment. Most of the setæ of the exopodites have
been removed, so that each remains as a curving, many-segmented organ,
transversely striated, with a continuous groove along the posterior
side. The setæ appear to be set in this groove, one for each of the
transverse ridges on the shaft.
A good deal of the test has been cut away on the left-hand side from
the thorax and pygidium, and the appendages exposed from above. Enough
of the dorsal shell has been cut away so that the anal opening is
exposed, and directly behind the pygidium, on the median line, is a
bilaterally symmetrical plate with serrated edges which appears to be
the appendage of the anal segment. (See pl. 3, fig. 4.)
_Measurements:_ The specimen is 17 mm. long, and 8 mm. in greatest
width (at the back of the cephalon). From the median tubercle to the
outer edge of the pleuron of the second thoracic segment the distance
is 3.7 mm. From the point of articulation to the distal end of the
spines on the dactylopodite of the second endopodite on the right-hand
side is 4.3 mm. The basipodite of this appendage is 1.5 mm. long, the
ischiopodite 1 mm. long, the meropodite 1.2 mm. long, the carpopodite
0.5 mm. long, the propodite 0.35 long, and the dactylopodite 0.15 mm.
long. On the left-hand side the endopodite of the first segment
projects 3 mm. beyond the pleuron, the second, 3.2 mm. At the back the
appendages extend a maximum distance of 2.5 mm. behind the pygidium.
The median spinose process of the anal segment extends 0.75 mm. behind
the pygidium, and is 1.6 mm. in greatest width.
Specimen No. 204 (pl. 3, fig. 1; pl. 4, fig. 6; text fig. 42).
Illustrated: Amer. Jour. Sci., vol. 13, 1902, pl. 2, figs. 4, 5
(reproduced from photographs).
This specimen, which is developed from the dorsal surface, shows
especially well nine appendages of the left side. The first represent
the last segment of the cephalon; the remainder belong to the thorax.
As is usual, the exopodites of these appendages overlie and curve
behind the endopodites. All the exopodites have lost their setæ and
the segments of the endopodites are flattened by crushing. The
endopodites, while retaining only one or two of the movable spines,
have the cup-like bases of from two to four on each of the visible
segments, namely, the meropodite, carpopodite, propodite, and, in one
case, the dactylopodite. These appendages, although really marvellous
in preservation, are of such small size and react so badly to light
that their study is very difficult, and Professor Beecher, who had
observed hundreds of specimens through all stages of the laborious
process of cleaning the matrix from them, undoubtedly was much better
equipped to interpret them than any other person.
The drawing is made on the assumption that the appendages are
displaced and all moved uniformly outward so that the distal ends of
the coxopodites emerge from under the pleural lobe, whereas these ends
would normally be under the dorsal furrow, and the distal end of the
ischiopodite should reach the margin of the pleural lobe. While it
seems very remarkable that it should happen, that all the appendages
should be so moved that they would lie symmetrically a few millimeters
from their normal position, nevertheless it is found on measuring that
they bear the same proportion to the length and width that the
appendages of other specimens do, thus indicating that Professor
Beecher's interpretation of them was correct. I am unable, however, to
see the coxopodites which he has drawn as articulating with the two
branches of the limb.
[Illustration: Fig. 42.--_Triarthrus becki_ Green. Appendages of
specimen 204. Inked in by Miss Wood from the original tracing. × 10.]
This individual shows, better than any other, the connection of the
exopodite with the endopodite. Even though the coxopodites are gone,
the two branches of each appendage remain together, showing that the
basipodite as well as the coxopodite is involved in the articulation
with the exopodite. Just what the connection is can not be observed,
but there seems to be a firm union between the upper surface of the
basipodite and the lower side of the proximal end of the exopodite, as
indicated diagrammatically in text figure 33.
_Measurements:_ The specimen is 20 mm. long and 9 mm. wide at the back
of the cephalon. From the tubercle on the middle of the first segment
of the thorax to the tip of the corresponding appendage the distance
is 8 mm. The entire length of the exopodite of the first thoracic
segment is 4.6 mm. The exopodite of the appendage belonging to the
seventh segment is only 3.5 mm. long. The pleural lobe is 2.5 mm. wide
at the front of the thorax.
Specimen No. 205 (pl. 2, fig. 4).
Illustrated: Amer. Jour. Sci., vol. 13, 1902, pl. 5, figs. 2, 3
(photographs).
This is a small imperfect specimen, developed from the ventral side.
It retains the best preserved metastoma in the collection, but was
used by Professor Beecher especially to illustrate the convergent
ridges on the inside of the ventral membrane in the axial region of
the thorax. These ridges are very low, and on each segment of the
thorax there is a central one, outside of which is a pair which are
convergent forward, making angles of 35 to 45 with the axis.
The metastoma is shaped much like the hypostoma of an _Illænus_. It is
convex, nearly semicircular, with the straight side forward, and there
is a continuous raised border around the curved sides and back. This
border is separated from the central convex body by a deep linear
depression.
The hypostoma is also rather well preserved and has a narrow, slightly
elevated border at the sides and back.
_Measurements:_ The incomplete specimen, from which only a very small
portion of the length is missing, is 9 mm. long. The metastoma is 0.45
mm. long and 0.58 mm. wide.
Specimen No. 214 (pl. 1, fig. 2; pl. 3, fig. 6).
This is a large specimen, developed from the ventral side. It shows
the antennules and some other appendages of the head, but derives its
special interest from the excellent preservation of a few of the
exopodites, which are turned back parallel to the axis of the body and
lie within the axial lobe.
The shaft of the exopodite is made up of numerous short segments which
at their anterior outer angles are produced into spines, and which
also bear movable spines along the anterior border. As shown in
several other specimens, the exopodite ends in a more or less long
spoon-shaped segment bearing on its lower surface a broad groove. No
setæ appear to be attached to this, but both anterior and posterior
margins bear numerous small, apparently movable spines. From the
groove along the ventral side of the remainder of the exopodite arise
numerous long slender filaments which become progressively shorter
toward the tip. This specimen shows that they are not cylindrical, but
are flattened along opposite faces, at least at their distal ends.
While no connection can be seen between adjacent setæ, they seem to
stay together like the barbs on a feather.
_Measurements:_ Length, 33 mm., width at back of cephalon, 16 mm.;
from front of cephalon to back of hypostoma, 6 mm.
Specimen No. 219 (pl. 2, fig. 6; pl. 4, fig. 4).
Illustrated: Amer. Jour. Sci., vol. 13, 1902, pl. 4, fig. 1, pl. 5,
fig. 4 (photograph and drawing).
The endopodites of most of the appendages of the thorax are well
shown, and occasional portions of exopodites. The coxopodites are
long, flattened, and do not taper much. The anterior and posterior
edges of the basipodites of the endopodites of the first two segments
are approximately parallel, but on the succeeding endopodites the
basipodites and ischiopodites are triangular in form, with the apex
backward. In successive endopodites toward the posterior end, the
angle made by the backward-directed sides of the basipodites becomes
increasingly acute, so that in some of the posterior appendages this
segment is wider than long. The ischiopodite shows a similar increase
of width and angularity on successive segments, and the meropodites
and carpopodites also become wider on the posterior segments, and even
triangular in outline toward the back of the thorax and on the
pygidium.
Along the median portion of the axial lobe the specimen has been
cleaned until the inner side of the ventral membrane was reached. Here
the test shows on the inner surface at each segment of the thorax a
series of low ridges which are roughly parallel to the axial line, but
which really converge in an anterior direction. Between the ridges
are shallow canoe-shaped depressions, which have the appearance of
areas for the insertion of muscles.
_Measurements:_ Length, 31 mm.; width at back of head, 15 mm.;
distance, in a straight line, from point of insertion of the right
antennule to its tip, 14.25 mm.; it projects 12 mm. beyond the
cephalon.
Specimen No. 218 (pl. 6, fig. 3; text fig. 43).
This specimen is a large one, developed from the lower side, but
retains only the endopodites of a few appendages. The cephalon and
anterior portion of the thorax are missing.
Professor Beecher had a drawing made to show the appendages on the
right-hand side of the last two segments of the thorax, seen of course
from the ventral side. This drawing shows well the broadening of the
basipodite, ischiopodite, and meropodite, while the coxopodite is
thick and heavy, and the inner end of the gnathobase somewhat rugose.
Almost every segment of the endopodites has one or more pits for
insertion of spines, these being along the anterior or posterior
margins. The exopodites lack the setæ, but show no unusual features.
[Illustration: Fig. 43.--_Triarthrus becki_ Green. Drawing to
represent the writer's interpretation of the appendages of specimen
218. Drawn by Miss Wood. × 10.]
Specimen No. 222 (pl. 4, fig. 5).
Illustrated: Amer. Jour. Sci., vol. 47, 1894, pl. 7, fig. 3
(drawing).
A small specimen, developed from the lower side, and used by Professor
Beecher to illustrate the form of the segments of the endopodites of
the pygidium. In addition to this, it shows very well the form of the
endopodites of the thorax. All of the appendages on the specimen are
shifted to the left of their normal position. This specimen differs
from most of the others in that the segments of the endopodites do not
lie with their greatest width in the horizontal plane, but were
embedded vertically, with the posterior edge downward. From this
circumstance they retain their natural shape, and it is seen that they
are naturally flattened, with about the same thickness in proportion
to length and width as in some of the modern isopods (Serolis, for
instance). In even the most anterior of these endopodites (that of the
second segment) the ischiopodite, meropodite, and carpopodite are
triangular in shape, with the point backward, but in all the
endopodites at the anterior end of the thorax, the triangle has a very
obtuse angle at the apex, and the base is much longer than the
perpendicular. On the other hand, those of the pygidium, which were
figured by Beecher, have a number of short wide segments, all wider
than long, and, excepting the dactylopodites, triangular in form.
_Measurements:_ Length, 8.75 mm.; width at back of cephalon,
about 4 mm.
Specimen No. 230 (pl. 5, fig. 3; text fig. 44).
Illustrated: Amer. Jour. Sci., vol. 47, 1894, pl. 7, fig. 2
(drawing); Ibid., vol. 13, 1902, pl. 2, fig. 2.
[Illustration: Fig. 44.--_Triarthrus becki_ Green. Appendages of the
posterior part of the thorax and pygidium of specimen 230. Inked by
Miss Wood from a tracing made under the direction of Professor
Beecher.]
An entire specimen of medium size, developed from the ventral side. It
seems to have been the first one to yield to Professor Beecher any
satisfactory knowledge of the appendages of the pygidium. There are
five endopodites, all on one side, which appear to belong here. The
segments in this region are characterized by their short, wide,
triangular form. At the apex of each is a small tuft of spines or
short hairs, and the ventral surfaces of some of the endopodites show
pits for the insertion of spines.
_Measurements:_ Length, 21 mm.; width at back of cephalon, 10 mm.
Cryptolithus tessellatus Green.
Specimen No. 233 (pl. 7, fig. 1; text fig. 45).
This is the best preserved entire specimen. It is developed from the
lower side, and shows the hypostoma, antennules, and a few fragmentary
appendages of the cephalon, the outer portions of the exopodites of
thorax and pygidium on both sides, and the endopodites on the left
side.
The hypostoma is imperfectly preserved and is turned completely
around, so that the anterior margin is directed backward, and the
posterior one is so much in the shadow that it does not show well in
any of the photographs. The form is, however, essentially like that
of _Trinucleoides reussi_ (Barrande), the only other trinucleid of
which the hypostoma is known, except that the border does not extend
so far forward along the sides, and it is much smaller.
The antennules are not inserted close to the hypostoma, as in
Triarthrus, but at some distance from it, and, as nearly as can be
determined, directly beneath the antennal pits which are seen near the
front of the glabella in many species of trinucleids.
[Illustration: Fig. 45.--_Cryptolithus tessellatus_ Green. Drawing of
specimen 233, made by Professor Beecher. × 9. Below are parts of two
of the endopodites of specimen 236, showing the interarticular
membranes. × 41.]
The antennules are long, and are composed of far fewer and longer
segments than those of Triarthrus. In this specimen they converge
backward, cross each other and at the distal end are more or less
intertwined.
As is shown in the drawing and photograph, very little can be learned
from this individual about the other appendages of the cephalon. A few
fragments of exopodites on either side suggest that these members
pointed forward and were much like those in Triarthrus, but nothing
conclusive is shown.
The exopodites and endopodites of the left side of the thorax are best
preserved. The exopodites are above the endopodites, and only that
portion exposed from the ventral side which projects beyond the line
at which the endopodites bend backward. The endopodite on the left
side of the first thoracic segment is the best preserved. It shows
seven segments, the outer ones best. The coxopodite is short and
narrow, the basipodite somewhat heavier and longer, while the
carpopodite and propodite are the widest and strongest segments. The
propodite is triangular and flattened, like the segments on the middle
and posterior part of the thorax of Triarthrus. At the inner end of
the ischiopodite and meropodite are tufts of spines pointing inward
and backward. These are not shown on any of the photographs, but may
be seen with the light striking the specimen at the proper angle.
It is not possible to count the exact number of limbs, but one gets
the impression that on the left side of this specimen there are
twenty-one sets of appendages, six of which of course belong to the
thorax. On the thorax and anterior part of the pygidium, successive
endopodites show the propodites and dactylopodites becoming
progressively more slender and shorter, while the ischiopodites,
meropodites and carpopodites become shorter and more triangular, and
with increasingly large numbers of short spines on their posterior
borders. Back of the fourth endopodite on the pygidium it is not
possible to make out the detail, but the appearance is of an
endopodite consisting of short broad segments fringed at the back with
short spines, the ones at the very posterior end appearing to be
exceedingly short and rudimentary.
The exopodites are not so well shown as in some others but the setæ
are flattened and blade-shaped, and often bear numerous small spines.
_Measurements:_ Length (lacking most of the fringe), 10.5 mm. Width of
thorax, 10.5 mm. Length of hypostome, 1.41 mm., width at front, 1.46
mm. The distance from back of fringe to end of antennules is 5.4 mm.
If straightened out, the left antennule would be about 6.1 mm. long.
In the first 3.1 mm., there are only ten segments, so that the average
length of a segment is 0.31 mm. The distance from the inner end of the
endobase of the first segment of the thorax to the outer end of the
meropodite is 2.43 mm., and from that point to the end of the
dactylopodite 2.47 mm. making the total length 4.90 mm. These
measurements are taken from the photograph. Measurements taken from
Professor Beecher's drawing, which was made with the camera-lucida,
give a total length of 4.57 mm., the distance to the outer end of the
meropodite being 2.3 mm. and thence to the tip of the dactylopodite
2.27 mm. Detailed measurements of the segments, on the photograph, are
as follows: coxopodite, 0.321 mm.; basipodite, 0.78 mm.; ischiopodite,
0.68 mm.; meropodite, 0.642 mm.; carpopodite, 0.642 mm.; propodite,
1.01 mm., dactylopodite, 0.825 mm.
Specimen No. 235 (pl. 7, fig. 2; pl. 8, fig. 3; pl. 9, figs. 1, 2).
Illustrated: Amer. Jour. Sci., vol. 49, 1895, pl. 3, figs. 5, 6.
Specimens 235 and 236 were originally parts of an entire
_Cryptolithus_, but, as Professor Beecher has explained, the specimen
was cut in two longitudinally on the median line, and the halves
transversely just back of the cephalon, so that each now represents
one half of a thorax and pygidium. Both halves have been cleaned from
both upper and lower side, a perfectly marvelous piece of work, for
the thickness is no greater than that of a thin sheet of paper, and
the soft shale of the matrix has a very slight cohesive power.
Both sides of specimen 235 were figured, but the dorsal side was
apparently then somewhat less fully developed than at present. On
plate 9 are two figures in which specimens 235 and 236 are brought
together again, and both dorsal and ventral sides illustrated.
On the dorsal side, specimen 235 shows portions of three exopodites
which lie in a direction roughly parallel to the outer portions of the
endopodites on the lower side, that is, their direction if projected
would reach the axis in an acute angle back of the end of the
pygidium. The setæ stand at right angles to the shaft, and on a
portion of it 0.5 mm. long there are seven of them. This is a fragment
of an exopodite near the front of the thorax, and the setæ, which are
flattened, are about 1.63 mm. long.
On the ventral side this same specimen shows incomplete endopodites
and exopodites of about seventeen segments, six of which would belong
to the thorax and the remainder to the pygidium. The greater part of
the appendages belonging to the pygidium are exceedingly small (about
0.15 mm. long) and so incompletely exposed that the structure can not
be definitely made out.
The endopodites of the thoracic segments all lack the greater part of
their proximal segments and are all of practically the same form. They
turn abruptly backward at the outer end of the meropodite, and the
carpopodite of each is greatly widened, projects inward and is armed
with tufts of spines. The propodite and dactylopodite are wide,
flattened, and taper but slightly outward, the dactylopodite bearing
on its distal end a tuft of spines. On several of the endopodites, the
meropodites are visible and they bear on their inner ends fringes of
spines pointing inward. Behind these well preserved appendages the
proximal segments of several endopodites are visible, and a regular
succession of flattened, oval bodies armed with numerous
forward-pointing spines. These latter bodies Professor Beecher took to
be leaf-like exopodites, which they certainly resemble, and as they
lie beyond the line of endopodites they probably do belong to the
outer halves of the appendages.
The exopodites under the thorax are long, the shaft shows numerous
short segments, and is in each case bent backward, though not through
a right angle. They extend considerably beyond the endopodites. The
setæ do not diverge from the shaft at a right angle as on the dorsal
side of this same specimen, but at an acute angle, indicating that
they were not rigid. The individual hairs are broad and blade-shaped,
frequently with a linear depression along the median line, perhaps due
to collapse of the internal tube.
_Measurements:_ The greatest length of the fragment in its present
state is 5 mm. The dactylopodite of the second endopodite (without
terminal spines) is 0.18 mm. long, the propodite 0.23 mm. long and
0.15 mm. wide; the carpopodite is 0.24 mm. long and 0.38 mm. wide. All
measurements were made on the photographs.
Specimen No. 236 (pl. 7, figs. 3-5; pl. 9, figs. 1, 2; text fig. 45).
The right half of the same thorax and pygidium as specimen No. 235.
The specimen is cleaned from both upper and lower sides and, the
dorsal test being removed, reveals the long blade-like setæ of the
exopodites, each blade being concave along its median line. They are
long on the exopodites of the thoracic segments, but become shorter,
without, however, any visible change of form on the pygidium. Although
the posterior end is not well preserved, one gets no suggestion from a
study of this side of the specimens that the exopodites of the
posterior end are in any striking way different from those of segments
further forward. The tips of some of the setæ show minute spines, one
to each blade.
On the ventral side are a number of endopodites, but they are more
fragmentary than those of the other half of the specimen. Some of the
exopodites are well shown, the blades being in all cases broken from
the shaft. Two of the endopodites of this specimen are of especial
interest, as they have interarticular membranes between the last three
segments. Professor Beecher made a drawing of one of these which he
placed under his pen drawing (text fig. 45).
_Measurements:_ The specimen is 5 mm. long from the front of the
second thoracic segment to the end of the pygidium. The setæ on the
exopodites of the anterior thoracic segments are 1.7 mm. long, as
exposed from the dorsal side. Some of those on the posterior part of
the pygidium, only incompletely exposed, are 0.31 mm. long.
[Illustration: Fig. 46. _Cryptolithus tessellatus_ Green. A part of a
thorax and pygidium, showing appendages. Drawn by Professor Beecher.
Specimen 238. × 10.]
The dactylopodite of the first endopodite showing the articular
membranes is 0.23 mm. long and 0.13 mm. wide. The propodite is of the
same length and 0.17 mm. wide. The interarticular membrane between
them is 0.066 mm. thick. The spines on the dactylopodite of this
appendage are 0.15 mm. long. All measurements were made on
photographs.
Specimen No. 238 (pl. 8, fig. 4; text fig. 46).
A triangular specimen consisting of the greater part of a pygidium and
parts of all the thoracic segments. Under the thorax the specimen has
been so cleaned that the outer portions of the endopodites are well
shown, while under the pygidium the greater part of the endopodites
seem to have been removed, disclosing the setæ of the exopodites. As
in other specimens, the endopodites of the thorax turn backward at the
distal end of the carpopodite, which is broad and curved, and bears a
tuft of spines on the posterior margin. The dactylopodites seem to
preserve their natural shape, and are very nearly cylindrical in form.
Under the pygidium are several sets of overlapping fringes of setæ of
exopodites, and along the edge of the dorsal furrow, a number of
fragments of segments of what may be coxopodites while with them are a
number of fragmentary shaft of exopodites.
_Measurements:_ The pygidium is 3.3 mm. long, the thorax 3 mm.
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1916.--Ann Rept., Secretary Smithsonian Inst, for 1915, pl. 9.
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Watase, S.
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(footnote).
Woodward, H.
1870.--Note on the palpus and other appendages of _Asaphus_, from
the Trenton limestone, in the British Museum. Quart. Jour. Geol.
Soc., London, vol. 26, pp. 486-488, fig. 1. Abstract in Geol.
Mag., dec. 1, vol. 7, p. 292, also in Nature, vol. 2, p. 94.
1871.--On the structure of trilobites. Geol. Mag., dec. 1, vol. 8,
pp. 289-294, pl. 8.
1884.--Notes on the appendages of trilobites. Geol. Mag., dec. 3,
vol. 1, pp. 162-165, 2 text figs.
1895.--Some points in the life history of the Crustacea in early
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pp. lxx-lxxxviii, 1 pl.
* * * * *
PLATE 1.
Photographs of _Triarthrus becki_, made by C. E. Beecher.
Fig. 1. Specimen 213. The dorsal test has been removed from the
glabella, revealing the outline of the posterior end of the hypostoma,
the proximal ends of the antennules, the gnathites, and incomplete
endopodites of some appendages, × 5.43.
Fig. 2. Specimen 214. The head of a complete large specimen. Part of
the thorax is shown on pl. 3, fig. 6. Note especially the form of the
segments of the endopodites and of the anterior coxopodite on the
right side, × 7.33.
Fig. 3. Specimen 217. This specimen shows better than any other the
form of the gnathites of the cephalon. Note also the setæ of the
exopodites under the cheek at the right. The appearance of a hook on
the posterior gnathite on the right may be accidental, but it does not
show broken edges, × 6.85.
Fig. 4. Specimen 215. The ventral side of the cephalon of a small
entire specimen. Shows well the form of some of the gnathites and a
few of the endopodites. Note the unusual position of the antennules. ×
7.63.
Fig. 5. Specimen 226. This specimen did not photograph well, but is
important as showing the exopodites and endopodites emerging from
under the cephalon. × about 6.
PLATE I.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 2.
Photographs of _Triarthrus becki_, made by C. E. Beecher.
Fig. 1. Specimen 201. The entire specimen, details of which are shown
in pl. 3, fig. 4 and pl. 4, figs. 1, 2. The dorsal test has been
removed from the anterior segments on the right side. × 4.12.
Fig. 2. Specimen 206. A small individual with the endopodites, and the
exopodites minus their setæ; well preserved on the left side. Note the
position of the antennules. The course of the facial suture is
unusually well shown. × 10.
Fig. 3. Specimen 210. The specimen which served as the main basis for
Professor Beecher's first figure of the appendages of the thorax,
specimen 206 (fig. 2, this plate) having supplemented it. Note the
"normal" position of the antennules and the extension of the
appendages from beneath the pleural lobe. Specimens with the
antennules in this position may possibly be males. × 4.
Fig. 4. Specimen 205. A small specimen with some of the appendages
preserved, especially toward the posterior end, but particularly
valuable for the unusually well preserved metastoma. × 11.
Fig. 5. Specimen 211. A small cephalon, cleaned from the ventral side,
and showing well the gnathites which approach each other unusually
closely on the median line. × 10.5.
Fig. 6. Specimen 219. An entire specimen of medium size, developed
from the ventral side. It shows particularly well the "normal"
curvature of the antennules, the change in form of the segments of the
endopodites from cephalon to pygidium, and, along the axial lobe, the
apodemes of the ventral integument. See also pl. 4, fig. 4. × 3.6.
PLATE II.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 3.
Photographs of _Triarthrus becki_, made by C. E. Beecher.
Fig. 1. Specimen 204. See also text fig. 42 and pl. 4, fig. 6. The
exopodites and endopodites of the first few segments of this specimen
are better preserved than those of any other revealing them from the
dorsal side, × 9.5.
Fig. 2. Specimen 220. A large individual exposed from the lower side.
It shows well the endopodites and part of the exopodites, and, rather
better than any other specimen, the endobases of the coxopodites. ×
2.4.
Fig. 3. Specimen 216. A small entire specimen showing considerable of
the detail of the appendages of the cephalon, and some of those of the
remainder of the body, × 7.4.
Fig. 4. Specimen 201. This figure shows the details of the appendages
of the left side and of the pygidium. Note the plate on the median
line back of the pygidium, the sockets for spines, and the terminal
spines on the anterior endopodites. See also pl. 2, fig. 1 and pl. 4,
figs. 1, 2. × 7.1.
Fig. 5. Specimen 207. One half of the posterior part of the thorax and
pygidium, showing exopodites and endopodites as seen from the dorsal
side, × 7.6.
Fig. 6. Specimen 214. The exopodites have been turned back nearly
parallel to the axis of the shell. Notice particularly the long
flattened setæ and the spinose spatula-shaped terminal portion of each
shaft. See also pl. 1, fig. 2. × 7.
PLATE III.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 4.
Photographs of _Triarthrus becki_, made by C. E. Beecher.
Fig. 1. Specimen 201. Another photograph, similar to fig. 4, pl. 3,
but showing more clearly some details of spines on the endopodites. ×
12.66.
Fig. 2. Specimen 201. Three appendages on the right side of the
thorax. See also pl. 2, fig. 1 and pl. 3, fig. 4. × 12.66.
Fig. 3. Specimen 223. A small crushed specimen which nevertheless
shows well the appendages of the right side of the thorax, developed
from the ventral side. Note coxopodites, exopodites, and endopodites,
and that all appendages are moved equally laterally from their
original position. × 11.4.
Fig. 4. Specimen 219. Another photograph, with different lighting, of
the individual shown in pl. 2, fig. 6. This print brings out better
the coxopodites and the folds of the ventral membrane. × 3.23.
Fig. 5. Specimen 222. This specimen is interesting, because it shows
the endopodites in what is probably their natural position, that is,
in a plane nearly vertical to the plane of the body, instead of being
flattened down, as is usually the case. The appendages under the
pygidium are unusually well preserved. × 12.
Fig. 6. Specimen 204. Photograph of the entire specimen of which a
part is shown in text fig. 42 and pl. 3, fig. 1. × 4.5.
PLATE IV.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 5.
Photographs of _Triarthrus becki_, made by C. E. Beecher.
Fig. 1. Specimen 209. Photograph of the pygidium shown in pl. 6, fig.
2. This specimen shows especially well the way in which the exopodites
of the pygidium decrease in length backward, × 11.5.
Fig. 2. Specimen 229. The under side of the posterior end of a
medium-sized specimen, showing the appendages, especially the
endopodites. On and among the limbs are scattered numerous minute
spheres of pyrite, of the kind usually known as "trilobite eggs." They
do not show very well in the photograph, but can be made out much more
clearly with a hand lens, × 12.
Fig. 3. Specimen 230. A specimen showing the appendages of the
posterior part of the thorax and the pygidium. The same individual is
also shown in text fig. 44. Note particularly the form of the segments
of the endopodites, and the spines on them, × 13.
Fig. 4. Specimen 227. The small doubly curved bodies shown in this
figure lie under the axial portion of the cephalon and anterior part
of the thorax. The specimen still has a very thin coating of matrix
between it and the shell. Whether the curved bodies have anything to
do with the trilobite is not known, × about 12.
Fig. 5. Specimen 221. A small individual which shows well the
exopodites of the posterior part of the thorax. Note the spatulate
terminations and the spines of the shaft, × 11.
Fig. 6. Specimen 202. Posterior part of the thorax and pygidium,
showing endopodites and exopodites projecting under the dorsal test.
Note the spiniferous plate on the median line, and the large opening
in the anterior portion of it. × 9.75
PLATE V.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 6.
All figures except 4 and 5, from photographs by C. E. Beecher.
Fig. 1. _Triarthrus becki_. Specimen 203. A well preserved small
individual, showing the appendages of the right side of the thorax. ×
11.46.
Fig. 2. _Triarthrus becki_. Specimen 209. A well preserved individual,
showing the antennules and some appendages of thorax and pygidium. For
detail of the pygidium, see pl. 5, fig. 1. × 4.
Fig. 3. _Triarthrus becki_. Specimen 218. Ventral side of the pygidium
and greater part of the thorax of an individual of medium size. Note
especially the relation of exopodites to endopodites of the last two
thoracic segments. A drawing of these appendages is shown on text fig.
43. × 4,3.
Figs. 4 and 5. Endopodites, probably from a species of _Calymene_.
These specimens, with several others, are on a small slab of limestone
from the Point Pleasant (Trenton) beds opposite Cincinnati, Ohio.
Specimen in the U. S. National Museum. Photographs by R. S. Bassler.
Fig. 6. _Acidaspis trentonensis_ Walcott. Both the specimen, No. 245,
and the photograph are poor, but show that in this genus the
endopodites are like those of Triarthrus. × 8.5.
Fig. 7. _Cryptolithus tessellatus_ Green. Specimen 234. This specimen
shows well the backward directed antennules and also the outer
segments of some of the cephalic endopodites. × 11.
PLATE VI.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 7.
Photographs of _Cryptolithus tessellatus_ Green, made by C. E.
Beecher.
Fig. 1. Specimen 233. The best preserved individual, the one from
which Professor Beecher's drawing (text fig. 45) was made, and which
served as the principal basis for the restoration (text fig. 20). Note
the long, backward directed antennules, the abrupt backward turn of
the outer portions of the endopodites, the way in which the exopodites
extend beyond the endopodites, and the fact that alt are beneath the
cover of the dorsal shield. The hypostoma is turned entirely around.
× 10.9.
Fig. 2. Specimen 235. Half of the thorax and pygidium, with the
appendages revealed from the ventral side. Note the abrupt manner in
which the outer portions of the endopodites are turned backward. See
also pl. 8, fig. 3, and pl. 9, fig. 1 (right half). × 14.45.
Fig. 3. Specimen 236. Detail from fig. 4, to show the blade-like setæ
of the exopodites and the numerous terminal spines of the endopodites.
× 30.
Fig. 4. Specimen 236. The appendages of the thorax and pygidium, seen
from the lower side. Specimen 236 is the right half of the same
individual from which specimen 235 was obtained. Note the
interarticular membranes between the segments of the endopodites and
the blade-like setæ of the exopodites. See also pl. 9, fig. 1 (left
side). × 19.
Fig. 5. Specimen 236. The same specimen, seen from the dorsal side,
showing, when the test is removed, the long blade-like setæ of the
exopodites. See also pl. 9, fig. 2 (right half). × 19.
PLATE VII.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 8.
Photographs of _Cryptolithus tessellatus_ Green, made by C. E.
Beecher.
Fig. 1. Specimen 231. A nearly complete individual, cleaned from the
ventral side and showing obscurely the hypostoma and fragments of
numerous appendages. Note the lines of appendifers along the sides of
the axial lobe. × 11.
Fig. 2. Specimen 232. Although this is not very well preserved, it
shows more of the cephalic appendages than any other. Even so, only
just enough is shown to indicate that they were similar to those on
the thorax. × 12.
Fig. 3. Specimen 235. Dorsal side of the appendages of the thorax and
pygidium. See pl. 7, fig. 2 for the ventral view. On pl. 9, fig. 2
(left side) is a drawing taken from the same specimen. × 11.
Fig. 4. Specimen 238. Part of a thorax and pygidium, seen from the
ventral side. The series of heavy segments shown in the upper part do
not belong to one appendage, but are the distal ends of several
endopodites. See also text fig. 46 for a drawing of this specimen.
× 18.
Fig. 5. Specimen 237. Pygidium and part of the thorax, with some of
the appendages. × 11.
PLATE VIII.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 9.
_Cryptolithus tessellatus_ Green. Upper drawing by C. E. Beecher;
lower drawing by Miss F. E. Isham, under the direction of C. E.
Beecher.
Fig. 1. Appendages of the thorax and pygidium, seen from the ventral
side. These are not restorations, but drawings from the halved
individual numbered 236 (right side of drawing) and 235. For
photographs of these specimens, see pl. 7, figs. 2, 4. × 20.
Fig. 2. Appendages of the thorax and pygidium, seen from the dorsal
side. Same specimen as in fig. 1. For photographs, see pl. 7, fig. 5,
and pl. 8, fig. 3. × 20.
PLATE IX.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 10.
From photographs made by C. E. Beecher.
Fig. 1. _Isotelus latus_ Raymond. Ventral surface of the specimen in
the Victoria Memorial Museum at Ottawa, Canada. Note the large,
club-shaped coxopodites and the more slender endopodites. The first
large coxopodite back of the hypostoma belongs to the last pair of
cephalic appendages. The coxopodite of the appendage in front of it is
seen turning in beneath the tip of the hypostoma. × 2.
Fig. 2. _Isotelus maximus_ Locke. The ventral side of the specimen
described by Mickleborough and now in the U. S. National Museum. The
tips of the hypostoma may be seen at the front, and the first two
pairs of coxopodites behind them belong to the last two pairs of
appendages of the cephalon. Note how much stronger the coxopodites are
than the endopodites. The appendages of the pygidium show but poorly,
× 1.45.
PLATE X.
HELIOTYPE CO. BOSTON
* * * * *
PLATE 11.
_Ceraurus pleurexanthemus_ Green. A restoration of the ventral surface
and appendages, made by Doctor Elvira Wood, under the supervision of
the writer, from data obtained from the translucent slices prepared
and described by Doctor Walcott. × 5.
PLATE XI.
HELIOTYPE CO. BOSTON
* * * * *
Transcriber's Notes
Small captioned text was not converted to ALL CAPS.
The numer 1 and capital I both look alike in the printed version.
Therefore, some of the volume, plate and other roman numerals may
have been incorrectly converted to 1.
Some tables were reformatted due to space considerations.