OF RECENT CROCODILIANS. 155 
The skull of the Alligator palpebrosus is easily known from that of this species even 
in the young by the cheeks of the former being flattened and nearly erect, and of the 
latter spread out, and in the supratemporal fossze being open, while in the Alligator they 
are closed even in the young specimens. 
Most probably it was from the examination of a skull of this Crocodile that the 
statement has arisen that in some Alligators the canine teeth sometimes fit into a notch 
in the upper jaw, and not into a pit as they normally do in that genus. I will not under- 
take to say that such an abnormal state does not exist in the genus Alligator; but 
I have not observed it. 
Hatcrosia ni@ra (Black African Crocodile). (Plate XXXI. figs. 4, 5, 6.) 
Krokodile noir du Niger, Adanson, MS., Mus. Paris. See Cuvier, Oss. Foss. iii. 41. 
Crocodilus niger, Latr, H. N. Rept. i. 510, from Adanson,. 
Crocodilus palpebrosus, var. 2, Cuvier, Oss. Foss. iii. 41, t. 2. f. 6 (part.). 
Crocodilus trigonatus (part.), Cuvier, Oss. Foss. iii. 65. 
African Black Crocodile, Gray, Rep. Brit. Assoc. 1862, Sections, 107. 
Osteolemus tetraspes, Cope, Proc. Acad. N.S. Philad. xii. 550. 
Crocodilus frontatus, A. Murray, Proc. Zool. Soc. 1862, pp. 139, 213, fig. head, t. 29. by Ford. Strauch, 
Syn. Croce. t. 1 (head, young). 
Halcrosia frontata, Gray, Aun. & Mag. Nat. Hist. 3rd series, x. 277. 
Hab. West Africa: Senegal (Adanson); Gaboon ; Old Calabar; Ogobai River (Cope). 
Figs. 11-14. Head and cervical and nuchal plates of young Halcrosia nigra 
