CROCODILIANS, LIZARDS, AND SNAKES. 1131 



are terrestrial. Lache.sis includes a lew species oC large size, and rlie 

 caudal ai)ex is much produced in auticipation of the rattle of the true 

 rattlesnakes. In Ancistrodon we have robust species of the ground, 

 the A. jnseivorns being, however, largely aiiuatic in habit. It is one 

 of the largest of the family. Sistrurus includes a few rather small 

 s])ecies, which prepare the way for the true rattlesnakes. The latter 

 are principally abundant in species in North America and north- 

 ern jNIexicQ. The heaviest of all venomous snakes is the Crotalns 

 (ulamanteuH of the southern regions of Xorth America, which attains a 

 length of 8 feet. Its bite is generally fatal. Other large and dan- 

 gerous species are the C. molossus of the United States and Mexican 

 boundary region, and the G. durissiiSj which inhabits the warmer regions 

 of the Neotropical realm. 

 Two subfamilies are readily distinguishable, namely: 



No joiuted epidermal caudal appendix Lacheainw. 



A jointed epidermal structure at the extremity of the tail Crotalina. 



The genera of this subfamily are as follows: 



a. Urosteges two-rowed. 



Top of head scaled ; urosteges four- rowed at end ; a caudal spine . . Lachesis Wagler. 



Like Lachesis, but a spinous scale over the eye Ophryacus Cope. 



Top of head with large imbricate shield-like scales Peltopelor Giinther. 



Top of muzzle scaled ; rest of head shielded Ihjpnale Cope. 



Top of head with nine shields; scales carinate Iritjonocephalus Oppel. 



Top of head with nine shields; scales smooth CaUo-selasma Cope.' 



aa. Urosteges one-rowed. 



Body and tail cyliudric, not prehensile; head scaly Iloihriopsis Peters. 



Body aud tail compressed, prehensile ; head scaly ; scales normal, 



lioihricchis Peters. 



Body and tail compressed, prehensile; head scaly; a row of scales outside the 

 superciliary shield Telenraspis ( "ope. 



Body and tail not prehensile; nine normal head-shitdds -.Jnc*s/rof?OH Beau\'ois. 



The genera of the above series which I have examined are Cophias, 

 Oj>hryacns, liothriojjsis, Teleuraspis, A>icLst)-odo7i. In all the hemipeuis 

 is calyculate, excepting in Ancistrodon, which is flounced, with a ten- 

 dency to form calyces opposite the sulcus in A. piscivonis. 



ANCISTRODON Beauvois. 



Ancistrodon Bairu, Serjjents N. Y., 1854, p. 13. — Copic, Proc. Aca<l. Xat. Soi. Phila., 



185!t, p. 3:3(5; Check-list N. Amer. Batr. Kept., 1875. p. 34. 

 Aijlixlrodon Beauvois, Trans. Amer. Phil. Soc, IV, 1799, p. 381. — Baird aud 



G IRAKI), Cat. N. Amer. Kept., Pt. 1, Serp.. 1853, p. 17.— Copk, Bull. U. S. Xat. 



Mus.,No.32, 1887, p.(i3. 

 Cenchris Dauoin, Hist. Nat. Reptiles, V, 1803. p. 3.58. — Wa(;i.kk. Nat. Syst, 



Amphib,, 1830, p. 175. 

 Toxicophis TiiOOST, Ann. Lye. Nat. Hist. X. Y., Ill, 1833. p. lUO, — Baikd and 



GiRARD, Cat, N. Amer. Kept,, Pt, 1, Serp,, 1853, p, 19. 



' Leiolejiis Dumi'ril and Bihrou, not of Cuvier. 



