CATALOGUE OF SHIELD REPTILES. 



1!) 



Fig. 10. 



Fisr. 12. 



Fig. 11. 



Fig. 13. 



>?r#J&" 



Halcrosia nigra, young. Head and cervical and nuchal plates. 



II. Nape with a broad fiat-topped shield formal of two 

 or three pairs of keeled plates, strongly keeled on each 

 side, and nearly continuous with the dorsal shield. 

 Legs fringed. Toes webbed. Abnormal Crocodiles. 

 a. Face broad ; nasal bone produced into the nostril. Alli- 

 gatoroid Crocodiles. 



6. HALCROSIA. 

 The premaxillary suture transverse, rather convex back- 

 wards. Nasal bones produced beyond the intermaxillary, 

 and forming a bony septum between the nostrils. The 

 palatine bone produced to the same level as the lateral 

 opening — that is, to the lateral inflection of the skull. The 

 face oblong, broad, without any ridge in front of the orbit. 

 Eyelids with two bony plates. Nuchal plates four, in a 

 cross row, strongly keeled. Dorsal plates in four series ; 

 the central broad, slightly keeled ; the outer narrow, di- 

 stinctly keeled ; sides with largo convex scales. 

 Halcrosia, Gray, Ann. Sf Mag. Nat. Hist. 3rd series, x. 



p. 273 ; Trans. Zool. Soc. 1869, vi. p. 152. 

 Osteolsemus, Cope, Proc. Acad. Nat. Sci. Philad. xii. p. 550. 

 Prof. Lilljeborg has described an Halcrosia Afzelii from a 

 specimen in the Swedish Museum, sent by Afzelius from 



Sierra Leone (Proc. Zool. Soc. 1867, p. 715) ; but it appears 

 to be only a slight variety of Halcrosia nigra. 



Mr. Cope claims priority for the genus Osteolmnus, and 

 states that his 0. tetraspis should not be identified with 

 Halcrosia nigra (Proc. Acad. Nat. Sci. 1867, p. 200) ; but 

 it appears to be only a slight variety. 



Halcrosia has the square head and elongated cervical 

 shield formed of single pairs of scutella, and the bony eyelids 

 of the Alligators with bony eyelids ; but it is a Crocodile, and 

 there are two bones in the eyelid instead of one as in 

 Caiman palpebrosus. 



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 foss;e being 

 open, while in the Alligator they are closed even in the 

 young specimens. Most probably it was from an exami- 

 nation 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 undertake to say- 

 that such an abnormal state does not exist in the genus 

 Alligator ; but I have not observed it. 



ii l' 



