560 THE AMERICAN NATURALIST. [Vor. XXXIV. 
nares. The palatine teeth are numerous and evident, and there 
is a decided bend in the palatine bones, in marked contrast 
with the feebler development of teeth in the adult 4. Zzezzuum, 
where also the palatines are not so strongly bent as here. In 
the lower jaw the dentary also bears an indistinctly double row 
of well-marked teeth, and directly behind it there is another 
row of teeth (splenial?), carried on a bony or cartilaginous sup- 
port, which appears to be entirely distinct from the dentary, 
though in close relation withit. The posterior row is not com- 
plete in the middle line. The floor of the mouth is pierced by 
the gill slits, and the tongue is only feebly developed. 
The trunk region is somewhat distended by the reproductive 
organs. Its wall is marked by the ‘costal grooves," as they 
are called by Cope (89), consisting of light, narrow myocommata 
and darker broad myomeres. The number of myomeres in- 
cluded between the front and hind limbs is twelve, as in A. ZZg7?- 
num. The proportion of the trunk to the post-abdomen is 
the same as in the adult A. ¢igrinum. The dorsal fin origi- 
nates on the level of the second costal ring, some distance be- 
hind the head. The position of this point of origin in the 
Mexican axolotl and in Baird's siredons, as indicated in the 
figure in Stansbury's report, is close to the head, but in Teget- 
meyer's figure and in the specimens from Montana the fin 
originates as in the Dakota specimen. The fin is not very 
high at any point, and in texture is not thin; in the Montana 
specimens the fin broadens out very much in the post-abdominal 
region, more so than-in any other recorded forms, and is very 
thin, so that the branchings of the blood vessels are very evident. 
The limbs are located here as usual, but the fore limb is 
shorter thàn in some of the allied forms, reaching only to the 
sixth myomere, while in the Montana axolotls I find that they 
reach the eighth myomere. The fingers are considerably flat- 
tened, and at their base the skin stretches across between them 
so as to produce a web; this result is further aided by the very 
broad and slightly flattened condition of the forearm. The 
same condition is noticeable in the hind limb. In the latter 
the typical number of toes, vzz., five, is found on the left side, 
but only four are present on the right ; this number is abnormal. 
