166 DE. 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 paii- interposed between the second 

 and thu-d pairs. 



Skull with the superior temporal fossfe obliterated, the circumjacent bones uniting, 

 the eyelid with a single large bony plate covering the whole upper surface. A^omer 

 not apparent on the palate. 



Caiman, Gray, Cat. Tortoises &c. Brit. Mus. 66, 1844 ; Ann. & Mag. Nat. Hist. 3rd series, x. 330. 

 Huxley, Proc. Luin. Soc. 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 Cu\-ier, 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 Latia synopsis of the species, which is appended 

 to the paper, they arc regarded as distinct, and the second one is called C. trigo- 

 natus. Yet MM. Dumeril & Bibron, in their work, persist in following Cmder'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 \e\-y 

 distinct Alligators with bony eyelids found in Tropical America; which agrees well 

 with the character that M. Cuvier and MM. Dumeril & Bibron give to the two varieties 

 of that species ; and these species ai-e, as Cuvier observes, as distinct from one another 

 as C. aniericaniis from C. vuhjaris. 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, whicli he calls A. gihhiceps, which, if it is 

 separable from A. trigonatus, must be distinguishable from it by \cry slight characters. 



The Black Crocodile [Ilalcrosia paljjebrosa) of West Africa has so much resemblance 



*x 



