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- 
eal. Crown covered with small keeled scales. Scales with tubercular or 
swollen keels. Tail without a rattle, pomted. 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. 
Croratus mutus Linné, 1766, Syst. Nat., ed. XT, 373. 
Lacuesis Mutus Daudin, 1803, Hist. Rept. 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 
small plate wedged between the second and third. Infralabials 15 
10), third large and below the pit, sometimes a 
16, 
anterior largest. Submentals one pair of large, followed by several pairs 
35 rows, outer 
of small ones. Scales lozenge-shaped, broad, keeled, in 33 
broader and faintly keeled, inner with tubercular or swollen keels. Ven- 
trals broad, 221—230. Anal entire. Subeaudals 33 
by small keeled seales under about one sixth of the length of the tail. 
35 pairs, followed 
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 
