SYNOPSES AND DESCRIPTIONS. 9 



contact with the labials. Labials about 20, infralabials 20 to 22. Scales 

 in 65 to 69 rows, outer broader. Ventrals 233 to 240; subcaudals 52 

 to 57. Brownish, varying from light to dark (in alcohol), with a dorsal 

 series of quadrangular brown spots, cmarginate anteriorly and posteriorly, 

 separated from the series of triangular brown spots on the upper portion 

 of the flank by an interrupted narrow line of light color, which is most 

 distinct opposite the spots. Upper spots of the flank larger and more 

 distinct. An irregularly placed series on the outer rows of scales and the 

 edge of the abdomen. Spots darkening toward the tail, often with lighter 

 centers. A brown line on the head from the frontal region to the neck. 

 A brown line from behind the angle of the mouth through the eye to the 

 loreal region, spreading toward its extremities. A bar from the eye to the 

 lip. A pair of spots on each side of the lower jaw. Rostral with a spot. 

 Scales irregularly punctulate or spotted. Mex. 



I have little doubt that this will eventually be degraded to the rank of a 

 variety. Specimens at hand from the Isthmus of Darien are intermediates 

 between this species and B. constrictor. 



Boa constrictor. 



Var. isthmica. 



Body stout, compressed ; head distinct ; snout broad, truncate ; tail short, 

 prehensile. Rostral large, broader near the upper edge, concave at the 

 sides and below, rounded above, surrounded by scales larger than the 

 others of the head. Nasal divided. Eye surrounded by eighteen or nine- 

 teen scales. Several larger scales in front of the oculars. Two rows 

 between oculars and labitils. Labials 22-23. Infralabials 25-27. Scales 

 small, flat, smooth, in 78 rows, outer broader. Ventrals narrow, 246. Sub- 

 caudals 57. 



Ground color light greyish (in alcohol). Pattern of markings as in B. 

 constrictor. Transverse brown bands of the back twenty-five, posteriorly 

 united by the darker margins with the triangular spot on the upper part 

 of the flank. Beneath the latter on the flank there is a series of oblong, 

 rounded spots, each enclosing a rounded spot of lighter color. A series of 

 more or less broken quadrangular black spots on each side of the belly 

 includes scales of the outer row. The spots unite on the tail so as to form 

 a dorsal and subcaudal row. A light brown band from rostral to neck 

 includes several light spots on the occipital region. A brown band with 



