210 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [1885. 



the liead is a little less than the distance from the snout to the gular 

 fold ; and is contained in tbe distance from the snout to the groin three 

 and six-tenths times. The distance to the gular fold is contained in the 

 distance to the groin three and two-tenths times. The depth of the 

 head, on a line joining the angles of the jaws, is a little less than one- 

 half its width. The gular fold does not overlap, as it does in some spe- 

 cies. It may have done so in life, but manipulation of the skin fails to 

 restore an overlapping fold. The upper jaw projects be.vond the lower. 

 Eyes of moderate size. External nares small; their distance apart 

 somewhat less than the width of the interorbital space. 



The tongue is not notably dift'erent from that of A. tigHnum. The 

 teeth are arranged in four series, which together form an inverted V, 

 the angle of which is very obtuse. The limbs of the V, as seen with the 

 unaided eye, appear nearly straight, and are seen to extend beyond the 

 internal nares along their external fissure. Examination with a lens 

 proves that the inner series are each slightly '^-"-^ shaped and so disposed 

 as to make the aiigle of the V rounded off. The outer series on each side 

 is nearly as long as tbe corresponding inner series, is plainly separated 

 from it, and nearly straight or slightly concave on the posterior side. 

 Inner nares more distant than the external. The body is somewhat 

 depressed, but has not the swollen appearance presented by A. opacum. 

 The distance from the snout to the axilla is just equal to that from the 

 axilla to the groin. There are eleven well-marked costal grooves. There 

 is a median furrow, not deep but distinct, beginning on the occiput 

 and running along the back, deepening on the sacral region and ending 

 over the middle of the vent at the commencement of the caudal crest. 

 The cloacal region is considerably swollen and is broad and rounded, 

 or slightly emarginato, behind. The distance from the groin to the pos- 

 terior end of the vent in this species is greater proportionally than in 

 any other of the genus, so far as I have been able to determine. It is 

 contained in the distance from the snout to the groin but three and one- 

 sixth times. 



The tail is equal in length to the distance from the snout to the be- 

 ginning of the vent. It is much compressed and rather high. It has a 

 well-developed keel, or crest, which begins immediately over the cloaca 

 and extends to the tip of the tail. The keel is sharp above and is 

 bounded below, on each side, by a shallow groove. Inferiorly the tail 

 is broadly rounded for its anterior third or more, and is traversed by a 

 median longitudinal groove. The remainder of its lower border is com- 

 pressed to a sharp edge. A transverse section of the tail, taken just 

 behind the cloaca, would form approximately an isosceles triangle whose 

 base would be about one-half its height. One-third of the distance back 

 toward the tip the height of the tail is three times its thickness. 



The limbs are well developed. The posterior are a little longer, some- 

 what stouter, and the foot broader than the same limbs of a specimen 

 of A tigrinum that measures the same distance from the snout to the 



