218 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



The branchial fissure is situated nearly as far posterior to the can- 

 thus oris as the latter is posterior to the end of the lower jaw. It is in 

 the anterior part of a fossa, and is bordered anteriorly and posteriorly 

 by a narrow free membranous lamina. A short distance behind and be- 

 low this is situated the anterior limb. The length of the limb is equal 

 to the interocular space ; in some specimens a little less. The humerus 

 makes an angle with the rest of the limb, but the foot is continuous 

 with the cubitus; it is divided into either two or three toes. The pos- 

 terior limb is larger than the anterior, measuring nearl3^ half as long 

 again. Its ]iosterior border originates a very short distance in front of 

 the anterior extremity of the vent. It is comi)ressed, and gently curved 

 inwards at the knee joint. It is directed posteriorly, not quite reach- 

 ing the posterior extremity of the vent. It is divided into two or three 

 digits. The vent is a longitudinal slit, witb a prominent margin. Its 

 internal face is densely pappillose within the marginal border. 



Measurements of No. 6300. 



M. 



Total length 886 



Length of tail 182 



Length to cauthus oris 047 



Length to hranchial fissure 077 



Length to fore limb 081) 



Length of fore limb 0175 



Length of hind limb 024 



Width between nostrils 008 



Width between eyes 018 



Width of head at canthus oris 045 



In specimens in alcohol the color is a dark slaty brown above and 

 slate colored below. Its colors in life are said by Dr. Holbrook to be 

 the same. 



I have united into a single species the AmpMuma means and A. tridac- 

 tyla in the above account. The description was made from a specimen 

 (No. G300) in which there are two toes on the anterior and three toes 

 on the po.-terior limb. In two specimens of the National collection on 

 the toes are 3-1 and 2-1 in front. In the numerous specimens (No. 

 7013) from Mississippi the toes are variable also, Mr. Eyder* has 

 pointed out that one specimen displays the digits | f ; a second | I5 a 

 third I in front ; others have the characters of the Means type, f |, and 

 others the Tridactyle character, f f. All are young and from the same 

 locality. Mr. Ryder concludes from these facts that the two supposed 

 genera must be united. In this I agree with him 5 and after a study of 

 the specimens in the National Museum and in my own collection, I be- 

 lieve that the two species on which these supposed genera rest are not 

 distinguishable. I find no characters peculiar to any set of individuals. 



Development — Prof. O. P. Hay has observed the habit of this spe- 



* Proceed. Phi la. Ac, 1879, p. 14. 



