166 DR. J. E. GRAY’S SYNOPSIS OF THE SPECIES 
scutella have two keels, in others only one; but this is no specific distinction ; it is not 
rare to find species with two keels on one side of the neck, and only one on the other. 
2. CAIMAN. 
Head high, flattened on the sides, angulated above. Orbits without any ridges. The 
eyelids smooth, strengthened with a large, single, internal bony plate. The dorsal and 
ventral scutella bony, articulated together, forming a dorsal and ventral shield; the 
gular and lateral ventral plates keeled, the abdominal ones smooth; the cervical 
scutella four or five pairs, with sometimes one or a pair interposed between the second 
and third pairs. : 
Skull with the superior temporal fossze obliterated, the circumjacent bones uniting, 
the eyelid with a single large bony plate covering the whole upper surface. Vomer 
not apparent on the palate. 
Caiman, Gray, Cat. Tortoises &c. Brit. Mus. 66,1844; Ann. & Mag. Nat. Hist. 3rd series, x. 330. 
Huxley, Proc. Linn. Soe. iv. 3. 
This genus has been divided into two species—one having the cervical shields two, and 
the other four in a cross series; in all the latter there are two in a cross series, with 
one or two interpolated between the shields. 
I have seen no specimen which agrees in the the nuchal shields with either of the 
figures in Cuvier, Oss. Foss., though our two species agree in other respects with his 
figures ; and how such species with distinct organic characters could be regarded as 
varieties, I am unable to learn. 
I cannot conceive what induced M. Cuvier in his ‘ Essay’ to consider the two South- 
American Alligators with bony eyelids varieties; for he justly observes, ‘‘ ‘The Crocodile 
of St. Domingo is not more distinct from the Crocodile of the Nile than these two 
varieties are from each other.” In the Latin synopsis of the species, which is appended 
to the paper, they are regarded as distinct, and the second one is called C. trigo- 
natus. Yet MM. Duméril & Bibron, in their work, persist in following Cuvier’s 
first idea of their being only varieties, and in regarding Adanson’s specimens as 
belonging to the second variety, and also in doubting if the “ two varieties,” are both 
from America. 
The specimen in the British Museum proves most distinctly that there are two very 
distinct ‘Alligators with bony eyelids found in ‘Tropical America; which agrees well 
with the character that M. Cuvier and MM. Duméril & Bibron give to the two varieties 
of that species; and these species are, as Cuvier observes, as distinct from one another 
as C. americanus from C. vulgaris. The heads of both these species are figured by Dr. 
? 
John Natterer in his ‘ Essay on American Alligators” in the Vienna ‘'Transactions.” 
This author also figured a third species, which he calls A. gidbiceps, which, if it is 
separable from A. trigonatus, must be distinguishable from it by very slight characters. 
The Black Crocodile (Lalcrosia palpebrosa) of West Africa has so much resemblance 
