14 PROCEEDINGS OF THE ACADEMY OP [1879. 



MORPHOLOGICAL NOTES ON THE LIMBS OF THE AMPHITJMIDJE, AS 

 INDICATING A POSSIBLE SYNONYMY OF THE SUPPOSED GENERA. 



BY JOHN A. RYDER. 



Little attention has apparently been given to the comparative 

 history of the limbs of the known species of Amphiuma. Very 

 young specimens do not seem to have been usually collected for 

 museums. I have had the opportunity to study such a series 

 varying from 6 to 8 inches long, and about ^th inch, or a little 

 more, in diameter; the} r were obtained in the vicinity of Biloxi, 

 Mississippi, and are the property of the Smithsonian Institution 

 at Washington. 



From these it appears that the digital elements of the limbs 

 are variable, or liable to variation in the same individual, so that 

 in some the number of digits (two) is characteristic of Amphiuma, 

 and in others (three) they are characteristic of Muraenopsis. This 

 blending of the characters of the two genera may be illustrated 

 as follows, indicating the number of digits on each limb by nume- 

 rals, arranged in fours, the first pair representing the digital for- 

 mula of the four limbs, thus: (1) f ; (2) ; (3) | f ; and (4) 

 \ | ; there was also a form which exhibited no outward indication 

 of toes on the front pair of limbs, the digits being inclosed in a 

 common investing integument ; this fifth form may be represented 



j 2 3 

 in this manner ^ It is plain from the foregoing, that at no very 



remote period the two forms which are now believed to character- 

 ize distinct genera were probably one and the same. The three- 

 toed form (Muraenopsis) is said to be confined to the Southern 

 United States, whilst the two-toed form (Amphiuma) is more 

 widely distributed, extending farther north, and also embracing 

 the distribution of the former. The digital formula of (1) is 

 Amphiuma in the front pair, and Muraenopsis in the hind pair of 

 limbs; that of (2) is Amphiuma on one side in the hinder pair, 

 and Muraenopsis on the other. Normal individuals of both genera 

 also occur, as in (3) and (4); while (5) represents the beginning 

 of the differentiation of a third generic type, if the number of 

 digits be good and sufficient to characterize genera. Prof. Cope, 

 who has probably handled more specimens of Amphibia than any 

 other American naturalist, informs me that he thinks these varia- 



