532 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 95 
We were unable to obtain material from the type locality at Santa 
Isabel. However, the figures of the species given by Velasco (loc. 
cit.) show a larger, highly colored animal and larger transformed speci- 
mens that appear different from the transformed young in this col- 
lection. It may be that we err in thus associating these forms. The 
matter cannot be settled at this time. 
‘We are of the opinion that the cause for specific differentiation of 
the species of ambystomid salamanders from the ancestral stock is 
largely the varied salt and acid content in the different permanent 
bodies of water occurring in the Valley of México. 
AMBYSTOMA LACUSTRIS, new species 
PuateE 18, Ficurss 1, 2 
Type —U.S.N.M. No. 117410, collected at Lake Zumpango, 
México, by Dr. and Mrs. Hobart M. Smith, March 3, 1939; re- 
cently transformed young. 
Paratypes—U.S.N.M. Nos. 116736-116755, collected at Lake 
Zumpango, by Dr. and Mrs. Hobart Smith; E.H.T.-H.M.S. Nos. 
22894-22910, Hobart M. Smith and E. H. Taylor, same locality. 
Diagnosis—A neotenic salamander of large size capable of trans- 
formation. Limbs relatively short in proportion to body length, 
the fingers of adults overlapping about length of second finger when 
limbs are adpressed; caudal fin small and part may be retained in old 
adults. Tail elongate, rather slender, a little less than snout to vent 
length; vomerine teeth arched, with a median diastema; choanae very 
large; elongate; body not elevated in the middle; tail widest at base. 
Description of type.—A large, recently transformed young (107 mm. 
from snout to vent; total length 198 mm.); gill slits closed, but three 
small beadlike remnants of the gills still visible on each side. Head 
thick posteriorly, the depth 20 mm. at angle of jaw; greatest width of 
the head (25 mm.) less than length to base of gills (28 mm.); eyes 
elevated somewhat, the interorbital width (9 mm.) a little less than 
length of snout (10 mm.); eye to nostril, 5.5 mm.; distance between 
nostrils, 10 mm.; gular fold prominent, the skin of chin folded longitu- 
dinally; vomerine teeth in two series beginning behind anterior level of 
choanae and running forward, tending to form an arch; however, there 
is a distinct diastema which is at a point bordering edge of the 
palatal pit; about 17 teeth in each series; palatine teeth diagonally 
placed, about 11 on each side, and practically continuous with the 
vomerine series. Choanae very large, elongate-oval, lying somewhat 
diagonally ; tongue beginning to develop but still very small; maxillary— 
premaxillary teeth about 55-55, the series continued to a point poste- 
rior to the posterior level of the choanae; mandibular teeth about 58-58. 
Many of the teeth have not yet pierced the gums; splenial teeth have 
disappeared; there is a remnant of an upper larval flap at the poste- 
