anterior edge of the maxillary is immediately posterior to the lateral
tip of the premaxillary (fig. 7). The maxillary is curved moderately
laterally and is not robust at its tip, but it becomes heavier about
one-third of its length posteriorly. A dorsomedian process begins at
about one-third of its distance from the anterior end; the prefrontal
articulates with this process. The process is broad and almost flat,
except that at its medial end, an elongate, rounded knob extends
ventrally. The dorsomedian process of the maxillary extends toward,
but does not meet, a lateral process from the palatine. The maxillary
teeth are set in sockets on the ventral surface of the bone. Just
posterior to the level of the last prediastemal tooth is the median
trans-palatine process that articulates with the anteromedian part of
the trans-palatine. Immediately posterior to this process, the
maxillary narrows slightly; then it broadens to form an obliquely
oriented knob. The posteroventral surface of the posterior knob of the
maxillary bears one or two enlarged maxillary teeth. (These teeth are
discussed further in the section on Dentition.) The anterolateral part
of the trans-palatine articulates with the dorsal surface of the
posterior knob of the maxillary. Toward the middle of its length, the
trans-palatine narrows considerably; then it broadens again and
articulates with the pterygoid. The palatine is slightly rounded at
its anterior end, which extends anteriorly to the posterior margin of
the vacuity containing Jacobson's organ. The palatine extends
posteriorly to the trans-palatine process of the maxilla, where the
palatine articulates with the pterygoid. A posterior pterygoid process
from the palatine projects posteromedially from the end of the
palatine and overlaps the anterior end of the pterygoid. Just less
than one-half the distance from the anterior end of the palatine,
there is a lateral process that curves ventrolaterally forming a blunt
tip posteriorly. Slightly more posteriorly and on the medial side of
the palatine, is a medial sphenoid process, which is thin, rather
broad, and curves ventromedially; ultimately it comes to lie near the
anterior part of the parasphenoid. The palatine teeth are set in
shallow sockets on the ventral edge of the bone. Of the bones of the
maxillo-palatal-pterygoid arch, those on the pterygoid extend farthest
posteriorly. The pterygoid is broad medially and posteriorly, although
pointed at its posterior tip. The trans-palatine articulates in a
broad line at about one-third of the distance along the lateral margin
of the pterygoid. Immediately posterior to this articulation, there is
a median ridge on the pterygoid; lateral to the pterygoid ridge is an
abrupt hollow, the pterygoid groove. Posteromedially, this groove
becomes gradually more shallow and disappears. The dorsal surface of
the pterygoid is rounded anteriorly and somewhat flattened
posteriorly, whereas the ventral surface is gently rounded along its
length, except that there is a high median crest. The pterygoid teeth
are situated in shallow sockets along this crest. The teeth diminish
in size posteriorly.
[Illustration: FIG. 8. The left mandible and associated
quadrate of _Conophis lineatus concolor_ (UMMZ S-788) showing
(A) lateral and (B) medial views. x 3. Teeth shown by means of
broken lines were represented only by their sockets.]
_Mandible._--The dentary (fig. 8) is compressed laterally and rounded
below. The teeth, which are longest about one-third of the way from
the anterior end of the dentary, are set in sockets on the medial side
of the bone. The posterior half of the dentary overlies the fused
surangular-prearticular part of the articular. Ventrally, the
posterior part of the dentary underlies the splenial, which is set in
a median trench within the dentary. Near the common suture of the
dentary and the splenial is the large inferior alveolar foramen;
completely within the splenial and ventral to the inferior alveolar
foramen is the anterior mylohyoid foramen. Posterior to the splenial
and also forming a part of the ventral surface of the mandible is the
wedge-shaped angular, which lies directly beneath the fused
surangular-prearticular. As has been implied, the articular, the
surangular, and the prearticular are fused. The prearticular part of
this bone forms a part of Meckel's canal. In the surangular part,
immediately posterior to the end of the dentary, is the large
surangular foramen. Lying in a longitudinal axis along the medial
surface of the articular is a high crest, dorsal to which is a deep
hollow. The lateral wall of the articular above this hollow is thin
and rounded dorsally; the ventral surface is uniformly round and
slightly curved dorsally, except that it ends with a short tympanic
crest, which projects beyond the articulation with the quadrate. Where
the quadrate articulates with the dorsolateral surface of the
posterior portion of the squamosal, the former is broad and has a high
mid-lateral crest, which extends about one-third of the distance down
the quadrate before disappearing. The columellar process (the place of
fusion of the columella) is about two-thirds of the way down the
medial surface of the quadrate. Ventrally the quadrate has a narrow
neck dorsal to its articulation with the articular. The articulation
is formed by two lateral flanges of the quadrate that fit over a
medial ridge formed by the articular.
Dentition
Teeth on the maxillary and pterygoid decrease in size posteriorly,
whereas those of the dentary do likewise except for the first one or
two that are usually slightly smaller than those immediately
posterior. The palatine teeth are subequal in size. The enlarged,
grooved teeth on the maxillary are in shallow sockets on the
posteroventral surface of the posterior knob of the maxillary. These
teeth point posteriorly. The grooves are deep and are situated
anterolaterally. One or two enlarged grooved teeth are present on a
given maxillary. There seems to be a correlation between the type of
preservation, the age of the snake, and the number of grooved teeth.
Old (large) individuals always have only one grooved tooth that is
rooted and functional, whereas some of the younger animals have two in
place. Usually replacement teeth are present in alcoholic specimens,
but these unrooted teeth are lost in the preparation of dried
skeletons. Thus, it seems that in _Conophis_ only one pair of grooved
teeth is functional at any one time, although usually replacement
teeth are present behind and beside the functional one. Some specimens
have one tooth in the medial socket on one side and one in the lateral
socket on the other. Replacement teeth on the maxillary and dentary
are present in the buccal tissue on the medial side of the bones,
whereas on the palatines and pterygoids, the replacement teeth are
present laterally. Apparently there are no significant differences in
dentition among the members of the genus _Conophis_.
Vertebrae
The fiftieth vertebra of _Conophis vittatus_ (UMMZ 82642) can be
described as follows: The neural spine is elongate, thin and low; the
posterior edge is sharply emarginate, and the anterior edge is only
slightly emarginate. The zygosphene is thin dorsoventrally; in a
ventral or dorsal view the zygosphene has a slightly concave anterior
edge, the flat surface of which is oriented ventrolaterally. The
centrum is elongate and triangular from below; it is widest at the
paradiapophyses and narrowest at the short condylar neck. The condylus
is directed posteriorly. The centrum, when viewed laterally, is
slightly concave and has prominent subcentral ridges that extend from
the median side of the paradiapophysial articular surfaces posteriorly
to the neck of the condylus. The paradiapophysial articular surfaces
are well developed and have two facets. The diapophysial surface is
larger and more spherical than the parapophysial one. The
parapophysial process projects beyond the parapophysial articular
surface and is nearly even with the lip of the cotyle, which is
slightly oval. The neural arch is slightly depressed; its width is
somewhat less than the width of the cotyle. The articular surfaces of
the postzygapophyses are oval and are directed posterolaterally. There
is a strongly developed concave interzygapophysial ridge. A
well-developed accessory spine extends laterally beyond the oval
articular facets of the pre-zygapophysis and forms a slightly
flattened, blunt spine. Excellent drawings of the middle thoracic
vertebra of _Conophis lineatus dunni_ from Honduras were published by
Auffenberg (1958:6).
Hemipenes
The hemipenes of _Conophis_ are moderately caliculate, having spines
covering the surface from the base to near the apex (fig. 9). These
spines are largest near the base and are reduced to small papillate
projections near the apex. The apex terminates in a small disc having
three to five laminae in _C. vittatus_ and one lamina in _C. lineatus
concolor_. The sulcus is bifurcate; the fork is near the base and
almost gives the appearance of two sulci on some specimens. Distally
the apices are widely separated, and the intervening space gives the
hemipenis a slightly bilobed appearance in some species (especially
_C. vittatus_) or a deeply bilobed appearance in others (especially
_C. lineatus concolor_).
[Illustration: FIG. 9. The everted left hemipenis of _Conophis
vittatus_ (UMMZ 82650). x 5.]
The everted hemipenis reaches posteriorly to the eighth subcaudal
scale. The sulcus bifurcates at the third subcaudal scale. The
situation is similar _in situ_ (Cope, 1895:pl. 28, fig. 2).
There are no apparent hemipenial differences among the species of the
genus _Conophis_. As can be seen in the above description, the
hemipenis of _C. vittatus_ is less bilobed and has a more pronounced
disc at the apex than the others. The hemipenis of _C. lineatus
concolor_ is most bilobed, but has the smallest apical disc. The other
species and subspecies vary widely within these extremes.
Food and Feeding
_Conophis_ eats mostly small lizards, especially _Cnemidophorus_. In
Mexico _Conophis_ occurs in semi-arid habitat where _Cnemidophorus_ is
common. A specimen each of _Conophis vittatus_ and _C. lineatus
lineatus_ were obtained while I was collecting _Cnemidophorus_. The
only record of _Conophis_ having fed on a warm-blooded vertebrate was
obtained in the course of this study, when I recovered from the
stomach of a _Conophis lineatus concolor_ (CNHM 36299) from Chichen
Itza, Yucatan, a heteromyid rodent (_Heteromys gaumeri_).
Ralph Axtell (personal communication) observed _Conophis_ actively
searching for food at dusk. His observations were made near
Tehuantepec, Oaxaca, and the snakes were seen to chase lizards of the
genus _Cnemidophorus_. Near Alvarado, Veracruz, in the late afternoon,
I watched a _Conophis lineatus lineatus_ follow a lizard into a hole.
Mittleman (1944:122) presents the only discussion of the mode of
feeding of a captive specimen of _Conophis lineatus_ ssp. When
presented with a _Thamnophis_ slightly smaller than itself, the
_Conophis_ struck, and within eight minutes immobilized the
_Thamnophis_. Within one-half hour the _Thamnophis_ was swallowed.
Three days later the _Conophis_ ate another _Thamnophis_, though still
distended from its first meal; nine days later it ate a _Storeria_. In
the course of several months, the _Conophis_ ate various toads and
hylids and two more _Storeria_. Apparently members of the genus
_Conophis_ do not constrict their prey, but rely upon a combination of
loss of blood and action of the venom to completely immobilize their
prey.
Ditmars (1931:pls. 26-27) showed three photographs of "_Conophis
lineatus_" (actually _Conophis pulcher_) ingesting another snake,
identified by him as a young _Ophis (= Xenodon) colubrinus_.
Effect of Poison
The rear fangs of these snakes are large for the size of the snake.
Various collectors have been bitten, and several reports of the effect
of the poison have been published. The snakes are aggressive and bite
constantly while being handled. A field companion, Dale L. Hoyt, was
bitten on the forefinger by a specimen of _C. l. lineatus_ and
immediately felt a burning sensation. The finger swelled, much as it
would if stung by a wasp, but it returned to normal size in about
twenty-four hours. Ditmars (1931:legend pl. 27) reported immediate
burning pain and a localized swelling, an inch in diameter and half an
inch high, which lasted for several hours. Mertens (1952b:83) reported
merely that the hand of the gardener at the Instituto Tropical in San
Salvador bled strongly for a full hour. Edward H. Taylor was bitten by
a specimen of _Conophis vittatus_ (Taylor and Smith, 1939:252); pain
and swelling lasted for some time. Taylor (personal communication) is
still troubled by damage incurred by that bite, which apparently
resulted in mechanical damage to the second joint of the middle
finger, for the joint swells when the finger is used or exercised.
William E. Duellman (personal communication) was bitten on the hand in
July, 1956. There was immediate pain and localized swelling, both of
which disappeared several hours later.
TAXONOMIC RELATIONSHIPS AND EVOLUTION
The genus _Conophis_ is known only from the Recent. Except that
_Conophis_ belongs to the subfamily xenodontinae and probably is of
New World origin, little is known about the relationships of the
genus. Auffenberg (1958) described a new genus and species of fossil
colubrid snake from the Miocene of Montana as _Dryinoides oxyrhachis_
and compared it with several recent genera. This specimen, of which
there is a relatively complete skull and a series of vertebrae, seems
most closely to resemble a specimen of _Conophis lineatus dunni_ (UF
7657) from Honduras, with which it was compared in basic osteology.
The two genera could be related, for the progenitors of _Conophis_
possibly inhabited much of North America in the Miocene.
Another possibility is that the main stock of the xenodontines reached
South America in earliest Tertiary times, and that the formation of
the Panamanian and Colombian seaways that separated South America and
Central America from the Late Paleocene to the middle of the Pliocene
left the _Conophis_ stock isolated in Middle America where members of
the genus dispersed through semi-arid habitats.
Turning our attention now to the species within the genus, instead of
the genus as a whole, _Conophis vittatus_ is readily set apart from
other members of the genus on the basis of the universal presence of
seven supralabials. In basic coloration it also differs, having no
stripe on the 1st scale-row, or spots on the venter, and a maximum of
four broad stripes on the body. The other species appear to be more
closely related; these make up the _C. lineatus_-group. _Conophis
nevermanni_ differs so much from the other species that it might be
placed in a separate group. Nevertheless, the basic striped pattern,
which is masked by the increased melanism of many specimens, indicates
that _nevermanni_ is more closely related to the _lineatus_-group than
to _vittatus_. The _lineatus_-group, thus, consists of _pulcher_,
_nevermanni_ and the three subspecies of _lineatus_. In this group the
color pattern is characterized by the high frequency of ventral
spotting, darkening of part of the supralabials, dark pigmentation on
the 1st scale-row, and more than four dark stripes on the body of
adults. _Conophis lineatus concolor_, on which the dark pigmentation
on the body apparently is secondarily lost, is an exception.
If differences in color pattern be used as an indication of the
relationships between the species and subspecies of the genus
_Conophis_, I would consider _C. vittatus_ the most divergent unit.
The subspecies of _lineatus_ closely resemble one another and, as a
unit, resemble _pulcher_ from which they differ primarily in the
position of the dorsalmost stripes. _Conophis nevermanni_ is more
divergent than is _pulcher_ from the species _lineatus_, but probably
is not so far removed from _lineatus_ as is _vittatus_.
In the light of what has been pointed out immediately above with
respect to resemblances of, and differences between, the species, an
hypothesis to account for their formation and for their presence in
the areas where they are today is the following: Concurrent with
climatic fluctuations in the Late Pliocene and Pleistocene, the
northernmost population differentiated into the species _vittatus_,
and has subsequently spread north and west from the region of
Tehuantepec, Mexico. During the same period _nevermanni_ became
isolated in northern Costa Rica.
The species _pulcher_ probably differentiated from the remaining
_lineatus_ stock during the Early Pleistocene orogenic upheaval in
Guatemala. The _pulcher_ stock was isolated on the Pacific Coastal
slopes of Guatemala, while _lineatus_ moved through the subhumid
corridor of northern Middle America into Mexico and southward toward
Costa Rica (Stuart, 1954a). In the Late Pleistocene and Recent,
_pulcher_ moved back across the central Guatemalan highlands occupying
its present range in northern Middle America. Primarily because of the
formation of unsuitable habitat (wet forest) that presently separates
the geographic ranges of populations of _lineatus_, this species
differentiated into three subspecies.
SUMMARY
The genus _Conophis_ Peters, 1860, contains four species. Three are
monotypic and the fourth has three subspecies, making a total of six
taxa.
The genus is characterized by maxillary teeth of equal size followed
by a diastema and two enlarged grooved fangs. The scales are smooth,
in 19 rows at mid-body, and 17 nearer the tail. The anal is divided,
apical pits are lacking, the head shields are normal for a colubrid,
and the hemipenis is bilobed having many large basal spines.
The six taxa are separated primarily on the basis of color pattern,
but characters of scutellation, including numbers of dorsals,
ventrals, caudals, and places of reduction of the number of dorsal
scale-rows, were analyzed.
Snakes of this genus are distributed throughout semi-arid environments
from southern Mexico southward into Costa Rica. They feed upon
lizards, primarily of the genus _Cnemidophorus_; in addition they are
known to eat small rodents and other snakes.
_Conophis_ is a member of the subfamily Xenodontinae and, as presently
understood, has no known living close relatives. A single specimen of
_Dryinoides_ from the Miocene of Montana has been compared with this
genus. The genus _Conophis_ is thought to have evolved in Middle
America. The present distribution and differentiation probably are
primarily the result of climatic fluctuations in Middle America, which
produced the areas of subhumid environment where _Conophis_ presently
lives.
LITERATURE CITED
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_Transmitted November 30, 1962._
29-5936
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