1, CAiTsus. 465 



Viperidss, Oausidse, Atractaspididse, Cope, Froe. Ac. Philad. 1864, 



p. 231. 

 Viperida, Strauch, Syn. Viper, p. 18, 1869. 

 Abothrophera, Garman, N. Amer. jRept. p. 104 (1883). 

 Viperina3, Boulenger, Faun. Ind., Sept. p. 418, 1890. 



Europe; Asia; Africa. 



Synopsis of the Genera. 



I. Head covered with large symmetrical shields as normal in the 



Colubridce ; mandibular teeth well developed ; eye moderate. 



Nostril between two nasals and the 'internasal ; pupil round ;. 



scales oblique on the sides 1. Causus, p. 465. 



Nostril in a single nasal ; pupil vertical ; scales not oblique. 



2. Azemiops, p. 470. 



II. Some or all of the head-shields broken up into small shields or 



scales ; mandibular teeth well developed ; eye moderate or 

 small, with vertical pupil. 



A. Lateral scales not smaller than dorsals, without serrated keels ; 



ventrals rounded ; subeaudals in two rows. 



Nasal in contact with the rostral or separated by a naso-rostral 

 shield ; postfrontal bone small .... 3. Vipera, p. 471. 



Nasal separated from the rostral by small scales ; a crescentic supra- 

 nasal ; postfrontal bone very large . . 4. Bitis, p. 492. 



Nasal separated from the rostral by small scales ; no supranasal. 



5. Pseudocerastes,p.501. 



B. Lateral scales smaller than dorsals, disposed obliquely, with 



serrated keels. 



Ventrals angulate laterally ; subeaudals in two rows. 



6. Cerastes, p. 501. 

 Ventrals rounded ; subeaudals single . . 7. Echis, p. 504. 



C. Lateral scales smaller than dorsals, slightly obHque, the keels- 



not serrated ; subeaudals single ; tail prehensile. 



8. Atheris, p. 508. 



ni. Head covered with large symmetrical shields ; mandibular 

 teeth reduced to two or three in the middle of the dentary 

 bone ; eye minute, with round pupU ; postfrontal bone absent. 



9. Atractaspis, p. 510. 



1. CAUSUS. 



Oausus, Wagler, Suit. Amph. p. 172 (1880) ; Gray, Cat. 8n. p. 33 

 (1849) ; Dum. 8f Bibr. Erp. 66n. vii. p. 1263 (1854) ; Cope, Proc. 

 Ac. Philad. 1859, p. 342 ; Peters, Peise n. Mossamb. iii, p. 143 

 (1882). 



Naja, part., ScTdeff. Phys. Serp. ii. p. 461 (1837). 



Disticnurus, Hallow. Joum. Ac. Philad, viii. 1842, p. 337. 

 VOL. in. 2 H 



