122 SYNOPSES AND DESCRIPTIONS. 



The following is taken from a Mexican specimen: Markings similar to 

 those of A. piscivorus, posterior part of body almost black, general appear- 

 ance very dark. Labials eight, third and fourth below the eye, separated 

 from it by the sub and postoculars (5). Two anteoculars. No loreal. The 

 specimen has five pairs of submentals, the anterior nearly twice the size of 

 those next following. Scales 'in 24 rows. Ventrals 135. Subcaudals one 

 pair, plus eleven entire, plus thirty-one pairs. Mexico. 



Lachesis. 



Daudin, 1803. 



Body long, back compressed, belly broad; head large, broad behind, 

 crown flat; tail short, pointed. Fangs and pit as in Crotalus. Pupil verti- 

 cal. Crown covered with small keeled scales. Scales with tubercular or 

 swollen keels. Tail without a rattle, pointed. Anal entire. Subcaudals 

 in two rows, except near the extremity, where they are small and keeled 

 like those of the upper surface. Brazils to Mexico. 



Lachesis mutus. 



Crotalus mutus Linne, 1766, Syst. Nat., ed. XII, '373. 

 Lachesis mutus Daudin, 1803, Sht. RepL V, 351. 



Resembles Crotalus durissus in form and squamation. Elongate, tapering 

 to neck and tail, flanks compressed, belly broad ; head large, broad behind, 

 crown flat; tail short, near one twelfth of the total, thick, pointed. Eye 

 moderate, pupil erect. Crown-shields small, keeled. Supraciliaries large. 

 A pair of internasals, separated by small scales. A few large scales about 

 the pit. Labials ten (9 — 10), third large and below the pit, sometimes a 

 small plate wedged between the second and third. Infralabials 15 — 16, 

 anterior largest. Submentals one pair of large, followed by several pairs 

 of small ones. Scales lozenge-shaped, broad, keeled, in 33 — 35 rows, outer 

 broader and faintly keeled, inner with tubercular or swollen keels. Ven- 

 trals broad, 221 — 230. Anal entire. Subcaudals 33 — 35 pairs, followed 

 by small keeled scales under about one sixth of the length of the tail. 



Yellowish-brown, with about twenty-eight (27 — 29) light-centered brown 

 lozenges on the back, more or less united along the vertebral rows, and 

 produced toward or upon the ventrals. Flanks between the dorsal lozenges 

 with or without spots or blotches of brown. Tail with 4 — 7 transverse 



