TACHYMENIS. 163 
6. Tachymenis decipiens, sp.n. (Tab. LIII. fig. A.) 
Hab. Costa Rica, Irazu (Rogers). 
Scales in seventeen rows. Upper labials seven, the third and fourth entering the 
orbit ; one preocular; temporal not in contact with postoculars; ventrals 165-173. 
Upper parts dark greyish-brown ; two yellow lines run along each side of the body and 
tail. Lower parts uniform yellowish. 
Rather slender in habit, the tail being long, about one-half of the length of the 
body. Snout rather short; eye of moderate size. Anterior frontals very short and 
small. Vertical shorter than the occipitals, but as long as or longer than the 
frontals; one preocular; one or two postoculars. Temporals 1+2, the anterior 
widely separated from the postoculars, the sixth labial forming a suture with the 
occipital. ‘Upper parts dark greyish-brown, with two narrow yellowish lines on each 
side, of which the lower runs along the outer series of scales; the upper takes its 
origin from a spot on each side of the neck, and is continued as a series of spots, of 
which one occupies the antero-lateral angle of the occipital, and the others the frontal 
shields. Upper labials brownish-black in the upper, and yellowish in the lower 
half. 
The largest specimen is 19 inches long without the tail, which is mutilated. 
As mentioned already on p. 105, this snake bears the closest resemblance to the 
aglyphodont Adlabes decipiens. Mr. Boulenger considers the latter to be synonymous 
with Liophis lateristriga (Berthold)= Urotheca lateristriga, Cat. Sn. ii. p. 181. The 
resemblance of the two snakes is certainly very great indeed, but the dental character 
of the genus Urotheca—* maxillary teeth 11 to 14, increasing in size posteriorly, followed 
after a short interspace by two enlarged ones”—does not apply to the types of A. deci- 
piens from Costa Rica, as far as the hindmost teeth are concerned ; these teeth are not 
enlarged, and not separated from the preceding by a larger interspace. I cannot 
describe such a dentition otherwise than isodont. But Mr. Boulenger is quite right 
in referring another specimen, from Ecuador, to Urotheca, which possesses a distinctly 
diacranterian dentition. 
Thus, in spite of the great outward similarity of Urotheca lateristriga and Ablabes 
decipiens, I am inclined to regard them as distinct; and in this I am confirmed by the 
number of preeoculars, which in the former is increased and may be as high as three, 
while A. decipiens has one only, sometimes with an additional small subocular. Also 
the yellow cross-band on the occipitals, which is so characteristic of A. decipiens, is 
absent in U. lateristrigqa. 
Since we know of the existence in Central America of two extremely similar snakes, 
one with an isodont (A. decipiens), the other (Tachymenis decipiens) with a glyphodont 
dentition, the presence of a third (Urotheca lateristriga) in Ecuador and Colombia 
with diacranterian teeth is not surprising. 
*21 2 
