surfaces not at all protuberant. The segments bear from three to five
pair of spines, with a row of three or four small intermediate spines;
there are, as usual, some little lateral upper rim spines; the dorsal
tufts contain some thick and thin spines mingled. _First_ cirrus is
short, and placed not quite close to the second pair; the basal segments
are broad and thickly paved with bristles. The _second_ pair is rather
short compared with the _third_ pair; a varying number of the basal
segments in both rami of both these cirri are protuberant, and are
thickly paved with bristles; such segments are more numerous and are
broader on the anterior rami than on the posterior rami. In _L. cauta_
alone, none of the basal segments in the posterior rami of the second
and third cirri are thickly paved with bristles. The pedicels of the
first three pair are irregularly covered with spines; those of the three
posterior pair have the spines arranged in a regular double line. Most
of the spines are doubly serrated.
_Caudal Appendages_ (Pl. X, fig. 23 and 24), multiarticulate, with thin
elongated segments fringed with short spines; in length generally
exceeding the pedicel of the sixth cirrus, and in _L. Nicobarica_
equalling half the entire length of this cirrus.
_Stomach_, destitute of cæca; oesophagus somewhat curled.
_Filamentary Appendages_, none.
_Ovaria_ filling up the peduncle and surrounding the sack, but not
extending up to the bases of the scuta and terga; I saw the ova only in
_L. truncata_; they were here oval and large, being nearly 9/400ths of
an inch in length.
_Penis_, elongated; vesiculæ seminales extending into the prosoma. I
noticed the ovigerous fræna only in _L. truncata_; here they were large,
with an almost bilobed outline; the margin and whole lateral surface
being covered with elongated cylinders, finely pointed, but not enlarged
at their extremities, as are the glands observed in most of the other
genera.
_Colours._--The posterior thoracic segments, the pedicels, the anterior
and dorsal surfaces of the segments of the cirri, the caudal appendages,
and the outer sides of the trophi are, in most of the species, more or
less mottled with dark purple; parts of the interior surfaces of the
valves in some of the species are coloured fine purple.
_Geographical Distribution._--The species are found all round the world
in the tropical seas; this fact may have some connection with the
presence of soft coral-reef limestone and of massive corals in these
seas. The presence, however, of _L. cauta_ on the shores of New South
Wales, shows that the genus is not strictly tropical.
_Affinities._--Lithotrya is a well-pronounced distinct genus; although
there is a considerable difference in the shape of the valves between
_L. dorsalis_ and _L. Valentiana_, at the opposite extremes of the
genus, the strict uniformity of the internal characters shows that there
are no grounds whatever for any generic separation; moreover, _L.
Rhodiopus_ neatly blends together these extreme forms. Indeed it is not
easy to imagine a better marked series of transitional forms, than those
presented by the terga, in passing from _L. dorsalis_ through _L.
Nicobarica_, _L. Rhodiopus_, and _L. truncata_, to _L. Valentiana_.
Lithotrya has most affinity to _Scalpellum villosum_ or to _Pollicipes
spinosus_ and _P. sertus_; though the affinity is far from close. In
these two species of Pollicipes, we have seen that large irregular
calcified spines are formed at the base of the peduncle, whereas in the
other Pedunculata the scales or spines are formed exclusively round the
upper margin of the peduncle. Lithotrya, as has been remarked by Sowerby
and other authors, exhibits some affinity to the sessile Cirripedes, as
shown by the calcareous basis,--by the manner in which the scuta and
terga are locked together,--by the two little fans of muscle attached to
near the basal points of the terga,--and perhaps by some of the
characters of the trophi; nevertheless, this affinity is far from being
well-marked, and I think is hardly so plain as in _Pollicipes mitella_.
1. LITHOTRYA DORSALIS. Pl. VIII, fig. 1 _a´_.
LITHOTRYA DORSALIS. _G.B. Sowerby._ Genera of Shells, April,
1822.
LEPAS DORSALIS. _Ellis._ Nat. Hist. Zoophytes, Tab. xv, fig. 5,
1786.
LITHOLEPAS DE MONT SERRAT. _De Blainville._ Dict. des Sc. Nat.,
Plate, fig. 5, 1824.
_L. scutis terga angustè obtegentibus: carinâ intùs concavâ: rostro,
duorum aut trium squamarum subjacentium latitudinem æquante: lateribus,
squamarum quinque subjacentium longitudinem æquantibus, superficie
internâ angustè ellipticâ: pedunculi squamis superioribus verticillum
secundum minus duplo superantibus._
Scuta, narrowly overlapping the terga: carina internally concave:
rostrum as wide as two or three of the subjacent scales: latera with
their internal surfaces narrowly elliptical, as long as five of the
subjacent scales: upper scales of the peduncle less than twice as large
as those in the second whorl.
Mandibles, with twice as many pectinations between the first and second
main teeth, as between the second and third teeth. Maxillæ without a
notch, edge nearly straight, and spines very numerous: caudal appendages
exceeding, by half, the length of the pedicel of the sixth cirrus.
Barbadoes, West Indies; Venezuela; Honduras; imbedded in
limestone; Mus. Brit. Cuming and Stutchbury.
The state of preservation of the valves in different specimens varies
greatly; generally only two or three, or even only the last-formed
shelly layer, is preserved, the upper ones having scaled off; in a few
young specimens, however, all the layers were perfect. The carina is
generally better preserved than the other valves, and hence the upper
part usually projects freely; in one specimen no less than ten zones of
growth were preserved in the carina, whilst the other valves consisted
of only three: the terga generally project rather more than the scuta.
As each growth-layer is thick, if the scaling process had not taken
place, all the valves would have projected greatly. The little teeth lie
close together on the prominent serrated rims, on each zone of growth.
The internal surfaces of the valves are roughened with small imbricated
points. Exteriorly the valves are covered with yellow membrane, with
rows, corresponding with each zone of growth, of very minute, yellow,
horny spines, generally having their tips bent over, and so made
hook-shaped. These spines are less than 1/600th of an inch in length.
_Scuta_, triangular; internally concave, with a large depression for the
adductor muscle; there is the usual small roughened internal knob, or
tooth, at the rostral angle of both the right and left hand valves.
Tergal margin straight, overlapping about one third of the entire width
of the terga.
_Terga_, irregularly oval, with the scutal margin straight; basal point
blunt, with the two sides placed at about an angle of 45° to each other;
the lower part of the carinal margin, immediately over the latera, (as
seen internally,) is slightly hollowed out. Exteriorly, towards the
bottom of the valve, from the overlapping of the scuta, of the latera,
and of the carina, only a narrow rounded ridge is exposed, which runs
down to the basal angle at about one third of the entire width of the
valve, from the scutal margin. Internally the valve is slightly concave.
The _Carina_ slightly overlaps the terga; internally concave; generally
with a large upper portion freely projecting; inwardly curved, without
any central crest or ridge; valve nearly as wide as the middle part of
the terga; inner growing or corium-covered surface, with its basal
margin, protuberant and arched.
_Rostrum_ (Pl. VIII, fig. 1 _a´_, _a_, and greatly magnified 1 _b´_)
very narrow; rarely more than two or three layers of growth are
preserved; the sides are deeply sinuous, owing to each zone widening
downwards; basal margin rounded; in width equalling about two and a half
of the uppermost scales of the peduncle, and about half as wide as the
latera.
_Latera_, small, placed obliquely, and parallel to the lower carinal
margin of the terga; longer axis equal to five of the uppermost scales
of the peduncle, and to nearly half the width of the base of the carina;
growing surface (or a section made parallel to the growth-layers,) is
narrow, elliptic, pointed at both ends, but the carinal half rather
thicker than the scutal half.
The _Peduncle_ varies in length, generally about twice as long as the
capitulum, in one specimen above thrice as long. The upper part as wide
as the capitulum, the lower part sometimes much attenuated. The
calcified scales in the uppermost whorl (Pl. VIII, fig. 1 _b´_) are only
slightly larger than those in the second whorl; the scales in the
succeeding three or four whorls, are considerably larger than those
below, which latter very gradually decrease in size, till, low down on
the peduncle, they are barely visible to the naked eye. In this lower
part, they may be called calcareous beads; they stand some way apart
from each other; they are nearly hemispherical, smooth, translucent, and
furnished with a conical fang; some of the smallest were 1/325th and
1/400th of an inch in diameter. The upper scales vary somewhat in the
outline, the most usual shape being sub-triangular, with the lower
margin arched and protuberant; and this margin, in the two or three
upper whorls, is crenated with teeth, which are conical and sharp, after
exuviation, but soon become reduced to mere notches. The scales in the
uppermost whorl are usually nearly quadrilateral; the imbedded portion,
or fang of each scale, is, in all, produced into a blunt rounded point.
The basal calcareous cup (fig. 1 _a´_ and 1 _c´_) is well developed, and
is sometimes even half an inch in diameter. Before the cup is formed,
there is a row of small, flat discs (fig. 1, and like those in fig. 2
_a´_) attached to the sides of the burrow: but a full account of these
parts of the peduncle, and of the burrowing habits of this species, has
been given under the generic description.
_Size and Colour._--Full average-sized specimens have a capitulum half
an inch in width and height; the entire length, with the contracted
peduncle, being about an inch and a half. Valves coloured dirty white,
with the enveloping membrane, when preserved, yellow. The outer maxillæ,
palpi, pedicels of the cirri, anterior faces of the segments, dorsal
tufts, caudal appendages, and penis, dark purple. Thoracic segments
brown. There is a purple spot between the bases of the first pair of
cirri.
_Mouth._--Labrum considerably bullate, equalling about half the
longitudinal diameter of the mouth; inferior part produced so as to
separate the mouth some way from the adductor muscle; crest with a row
of blunt teeth and hairs; central part depressed and flattened.
_Palpi_, rather large, separated from each other by only half their own
length; bluntly pointed, thickly clothed with spines.
_Mandibles_ (Pl. X, fig. 2), with twice as many pectinations, namely 15,
between the first and second main teeth, as between the second and third
teeth, namely about 7; inferior angle strongly and coarsely pectinated;
distance between the tips of the first and second main teeth,
considerably less than between the tips of the second tooth and of the
inferior angle; sides hirsute.
_Maxillæ_ (fig. 10), with the edge not quite straight, with the whole
inferior part slightly projecting; spines very numerous, thirty or forty
pairs; those close beneath the two upper great unequal spines, form a
tuft and are rather thinner than the others, as are also those near the
inferior angle; sides hirsute.
_Outer Maxillæ_, rather pointed, with the inner edge slightly concave,
continuously and thickly clothed with short spines; spines on the outer
edge long; there are also some minute, short, thinly scattered spines or
points on the sides. Bristles on all the trophi doubly serrated.
_Cirri._--The first pair is placed at a small distance from the second.
The segments in the three posterior pairs, support five pairs of very
long spines, with a row of (I believe) four small intermediate spines;
on the lateral upper edges, there are some short blunt spines; anterior
faces of the segments not protuberant; the dorsal tufts consist of thick
serrated, and of thin spines. The whole integument is hirsute with
minute pectinated scales. Two or three of the basal segments in the
sixth cirrus are confluent. _First cirrus_, anterior ramus rather
shorter and thicker than the posterior ramus; basal segments thickly
paved with serrated spines; in the posterior ramus, the six terminal
segments are not paved with bristles. _Second cirrus_ has the seven
basal segments of the anterior ramus very broad, and paved with
bristles; the eight terminal segments having the usual structure; in the
posterior ramus the three or four basal segments are similarly paved,
but to a very much less degree, and the remaining thirteen have the
usual structure. _Third cirrus_ has the six basal segments of the
anterior ramus very broad and paved, and the fourteen terminal ones of
the usual structure; in the posterior ramus, the three or four basal
segments are similarly paved, but to a very much less degree, and the
seventeen terminal ones have the usual structure. The pedicel of the
first cirrus has very few spines; those of the second and third cirrus
are thickly and irregularly clothed with spines; and those of the three
posterior pair have a double row with intermediate small spines. On the
antero-lateral faces of the pedicels of the second, third, and fourth
pairs of cirri, there is an elongated white swelling or shield.
Moreover, on the posterior thoracic segments, there are similar
white-coloured swellings, with the membrane more plainly marked with
scales than in other parts. The spines on the first three pairs of
cirri are coarsely serrated.
_Caudal Appendages_ (Pl. X, fig. 23), with numerous tapering segments,
almost equalling one and a half times the length of the pedicel of the
sixth cirrus. Each segment is elongated and somewhat constricted in the
middle, with its upper edge (fig. 24) crowned with short spines; in a
full-sized specimen there were seventeen segments.
2. LITHOTRYA CAUTA. Pl. VIII, fig. 3.
_L. scutis terga amplè obtegentibus: carinâ intus concavâ: rostro
squamarum subjacentium latitudinem vix æquante: lateribus, squamas
subjacentes sesquitertio superantibus; superficie internâ latè
ellipticâ: pedunculi squamis superioribus verticillum secundum pæne
quadruplo superantibus._
Scuta largely overlapping the terga: carina internally concave: rostrum
hardly as wide as one of the subjacent scales: latera with their
internal surfaces broadly elliptical, as long as two and a half of the
subjacent scales: upper scales of the peduncle nearly four times as
large as those in the second whorl.
Mandibles with an equal number of pectinations between the first,
second, and third main teeth: maxillæ notched, edge nearly straight:
posterior rami of the second and third cirri, with their basal segments
not paved with bristles: caudal appendages slightly exceeding in length
the pedicels of the sixth cirrus.
New South Wales, Australia, imbedded in a Conia, (unique
specimen,) Mus. Stutchbury.
Valves thin, white, translucent; upper layers of growth well preserved,
excepting on the terga. A large portion of the carina projected freely.
The teeth on the projecting margins of the growth-layers are broad,
blunt, and often stand rather distant from each other.
_Scuta_ (Pl. VIII, fig. 3 _a_), triangular, internally concave with no
distinct pit for the adductor muscle. The scuta largely overlap the
terga.
_Terga_ (fig. 3 _b_) approaching to rhomboidal; basal angle rectangular,
almost central, and consequently the exterior longitudinal ridge, which
is rounded, is likewise nearly central.
_Carina_, internally concave, with no trace of a central internal ridge
in the upper free portion; the growing or corium-covered surface is
transversely oval, and is as wide as the widest part of the terga.
_Rostrum_, exceedingly minute, enlarged at each zone of growth, not so
wide as the immediately subjacent scale on the peduncle.
_Latera_ (fig. 3 _c_), in width equalling two and a half of the upper
peduncular scales, or about one fourth or one fifth of the width of the
carina; growing surface, (or a section parallel to the layers of
growth,) broadly elliptic, pointed at both ends.
_Peduncle_, about twice as long as the capitulum; the scales of the
uppermost whorl are quadrilateral (fig. 3 _d_), and nearly four times as
large as those in the second whorl; these latter are about twice as
large as those in the third whorl, which are very little larger than the
small, almost equal-sized, equally distant, round beads scattered over
the rest of the peduncle, down to the basal cup. All these scales are
dentated, the upper rows most plainly and only on their basal margins;
the lower little beads are very slightly crenated round their entire
margins; they are mingled with star-headed spines (fig. 3 _e_) of yellow
chitine. Basal calcareous discs thin, plainly marked exteriorly by
concentric lines of growth, and covered by the usual yellow membrane,
including the horny, spindle-shaped bodies.
_Size and Colours._--The whole specimen, including the peduncle, was
only one fifth of an inch in length; the capitulum being 3/40ths of an
inch in width. I do not know whether the specimen had attained its full
size, but think this is probable, as a large-sized species would not
have made its habitation in one of the valves of so small a shell as a
Conia. Shell white, exterior membrane, where preserved, yellow, and
bearing small spines. Thoracic segments, the lower segments of the
second, third, and fourth cirri, all the segments of the first cirrus
and the trophi, slightly mottled with darkish purple.
_Mouth._--The teeth or beads on the crest of the labrum are blunt, few,
not very small, and equidistant.
_Palpi_, bluntly pointed.
_Mandibles_, with the three main teeth nearly equal in size; the
pectinations are equal in number, namely, only three between the first
and second, and the second and third main teeth; the inferior angle is
coarsely pectinated, with one central spine much longer than the others;
the distance between the tips of the first and second main teeth, equals
that between the second tooth and the inferior angle.
_Maxillæ_, with the two upper spines very large; beneath them there are
two small spines, and a considerable notch; the inferior part of the
edge is nearly straight, bearing about thirteen pairs of spines,
obscurely divided into two groups, the lower spines being smaller than
the upper ones. The upper convex margin is hirsute with long hairs.
_Outer Maxillæ_, blunt, with the inner margin slightly concave;
continuously, but thinly clothed with spines.
_Cirri._--The segments of the three posterior pairs bear four pairs of
spines, with the usual intermediate fine spines; dorsal spines thin and
thick mingled together. _First cirrus_, short, with the anterior ramus
rather the thickest and shortest; all the segments thickly paved with
bristles, except the two terminal segments, of which the ultimate one
bears some serrated spines of most unusual length, namely, equalling
within one segment the entire length of the ramus. I presume that these
spines serve as feelers. _Second cirrus_; anterior ramus much thicker
and considerably shorter than the posterior ramus; six basal segments
paved with bristles, the two terminal segments having the usual
structure; posterior ramus with all its nine segments on the usual
structure. _Third cirrus_, longer, to a remarkable degree, than the
second cirrus, with its anterior ramus having the four basal segments
paved, and the seven terminal ones on the usual structure; posterior
ramus with twelve segments, of which none are paved. The pedicels of the
second and third cirri thickly and irregularly clothed with spines. The
upper segments of the pedicels of all the cirri are unusually long.
_Caudal Appendages_, longer than the pedicels of the sixth cirrus, by
barely one third of their own length. Segments much elongated, seven in
number; I may add for comparison that each ramus of the sixth cirrus
contained, in this specimen, sixteen or seventeen segments.
_General Remarks._--It is difficult to give obvious characters,
(excepting the smallness of the rostrum compared with the scales on the
peduncle,) by which this species can be externally discriminated from
_L. dorsalis_, _L. Nicobarica_, and _L. Rhodiopus_; yet almost all the
valves differ slightly in shape. In this species alone, (the peduncle of
_L. Rhodiopus_ is not known,) the lower, microscopically minute,
bead-like scales of the peduncle are crenated, though obscurely, all
round. In the animal’s body, the diagnostic characters are strongly
marked;--the long spines on the terminal segment of the first
cirrus,--none of the segments in the posterior rami of the second and
third cirri being thickened and paved with bristles,--the pectinations
being equal in number between the main teeth of the mandibles,--are all
characters exclusively confined to this species.
3. LITHOTRYA NICOBARICA. Pl. VIII, fig. 2.
L. NICOBARICA. _Reinhardt_, Naturhist; Selskabet, Copenhagen. No.
I. 1850. Tab. I, fig. 1-3.[68]
[68] I am not at all sure that the proper title of the periodical
in which this species has been described, is here given. I am
greatly indebted to Prof. Steenstrup for sending me a separate
copy of the paper in question, written in Danish. I believe I am
right in identifying the specimen here described, from Timor,
with the species from the Nicobar Islands, named by Reinhardt,
_L. Nicobarica_.
_L. scutis terga angustè obtegentibus: carinæ cristâ internâ tenui in
parte superiore positâ: rostro conspicuo, squamarum sex subjacentium
latitudinem æquante: lateribus, superficie internâ triangulâ, squamarum
septem subjacentium latitudinem æquantibus._
Scuta narrowly overlapping the terga: carina with a slight central
internal ridge in the upper part: rostrum conspicuous, as wide as six of
the subjacent scales: latera, with their internal surfaces triangular,
as wide as seven of the subjacent scales.
Palpi square at their ends: mandibles with twice as many pectinations
between the first and second main teeth, as between the second and
third: maxillæ slightly notched, with the inferior angle slightly
prominent: caudal appendages more than twice as long as the pedicels of
the sixth cirrus.
Timor; Brit. Mus., (given by Cuvier to Leach); Nicobar Islands,
according to Reinhardt.
Capitulum as in _L. dorsalis_. The teeth on the prominent rims of the
valves are small and approximate; but the specimen was much worn.
_Scuta_, triangular, slightly overlapping the terga; the line of
junction between these valves slightly sinuous, the upper part of the
tergal margin of the scuta being slightly hollowed out, and the
corresponding upper portion of the margin of the terga being slightly
protuberant. Internally, there is a considerable depression for the
adductor muscle; and besides the usual knob at the rostral angle, there
is a trace of a knob at the baso-tergal angle.
_Terga_, as seen internally, irregularly rhomboidal, ending downwards in
a blunt point, of which the two sides, (neither being sensibly hollowed
out,) stand at about an angle of 45° to each other. Scutal margin, with
the upper part, (as above remarked,) slightly protuberant: near the
bottom of this margin, there is a very slight projection, answering to
the small knob at the baso-tergal angle of the scutum. Externally,
towards the basal angle, the narrow strip not concealed by the
overlapping of the latera and carina is square-edged, with the zones of
growth on it straight.
_Carina_, internally concave in the upper free part, with a slight,
central, internal crest, caused by the projection of each successive
zone of growth. The inner growing surface is almost pentagonal in
outline; with the basal margin square and truncated in the middle.
_Rostrum_ (fig. 2 _a_), rather conspicuous, many zones of growth being
preserved. It equals in width six of the subjacent scales of the
peduncle, but as these are rather smaller than elsewhere, the width
equals about five of the ordinary uppermost scales; compared with the
latera, it is nearly 5/7ths of their width.