124 SYNOPSES AND DESCRIPTIONS. 
Subecaudals bifid; 
scales in 27—29 rows asper. 
seales in 23—25 rows atrox. 
subcaudals entire; 
scales in 27 rows affinis. 
TRIGONOCEPHALUS ASPER. 
var. n. C. LANCEOLATI. 
Body long, tapering to head and tail; head large, broad behind, pointed 
and angular in front; crown flat, covered with small keeled scales. A pair 
of internasals, in contact behind the rostral; behind these on each side a 
larger plate rests against nasal, loreal and anteocular, but is separated 
from the Jarge supraciliary by a small scale. Rostral subquadrangular. 
Nasal in two parts, anterior larger. Loreal quadrilateral. Anteoculars 
two; upper much larger, sometimes divided; lower half as long, narrow. 
Suboculars narrow, fused, separated from the labials by a scale. Postocu- 
lars 2—3. Labials seven, posterior four large. Infralabials 1O—11. Sub- 
mentals one pair, not in contact with the mental. Scales keeled, in 27 
(27—29) rows. In large specimens the keel of the median rows is swollen, 
and does not reach the end of the scale. 
Reddish-brown, with Y-shaped marks of light color on the flanks, which, 
when opposed, inclose rhombs of the ground color or lighter. When reg- 
ularly opposed the pattern resembles that of Crotalus horridus or Lachesis 
mutus. Flanks lighter with one or more series of spots near the abdomen 
and upon its edge. Belly and sides of head yellowish, the former mot- 
tled posteriorly, the latter with a brown line from the eye to a point near 
the angle of the mouth. The specimens described were taken at Obispo, 
on the Isthmus of Darien, by Dr. Maack. Compared with specimens from 
Martinique and St. Lucia, they are distinguished by brighter colors and 
swollen keels. The pattern of markings is similar. The numbers and 
shapes of labials and other head-plates are the same. 
TRIGONOCEPHALUS ATROX. 
Coturpr atrox Linné, 1754, Mus. Ad. Fridr., Tab. 22, fig. 2, and Gmelin, 1788, Syst. Nat., 1107. 
Corutas arrox Merrem, 1820, Tent. Syst., 154. 
Body long, moderately slender, tapering to head and tip of tail; head 
broad behind, pointed in front, crown flat, covered with small keeled scales; 
