402 AMERICAN TESTUDINATA. Part II. 



It is true that this species very much resembles Tr. spinifer, LeS., in its 

 external appearance ; but, even without referring to their generic characters, they 

 may readily be distinguished in every stage of growth. The male of Platypeltis 

 ferox, with its projecting tail, is much more oblong ^ than that of Aspidonectes 

 spinifer, while the females are very similar in their rotundity. The tubercles 

 upon the shield are also larger and more numerous in the male ferox than in 

 the female ; just the reverse from what we see in spinifer. The young . ferox 

 (PI. 6, fig. 3) has two or three concentric black lines separating the pale margin 

 from the light brown colored back, which are sometimes preserved even to their 

 full-grown size ; in Asp. spinifer I have never observed more than one such 

 line, which disappears rather early. The back of PI. ferox is studded with well- 

 defined black dots, which become ocellated only in later years, and are finally 

 changed into dark blotches in the adult. The lower surface is entirely white, 

 even the lower surface of the feet, which are mottled, streaked, and dotted with 

 black in Aspidonectes spinifer. Asp. nuchali.s, and Asp. asper. Aspidonectes spinifer 

 never grows so large as ferox, and is only found in the Northern States, within 

 the same limits as Amyda mutica, with which it is mostly found associated. The 

 eggs of Platypeltis ferox (PI. 7, fig. 22) are of a somewhat smaller size than those 

 of Aspidonectes spinifer : they are, however, a little larger than those of Amyda 

 mutica, represented upon the same plate. 



The peculiar coloration of the lower surface of the feet, and the mottled 

 appearance of the lower part of the neck, of Asp. spinifer, first attracted my 

 attention as differing from Platypeltis ferox, and led me to a careful revision of 

 our Trionychidse. Trusting to the accuracy of previous writers, I have myself 

 believed, for a number of years, that there existed only two species of that 

 family in the United States, and that these two species belonged to one and the 

 same genus, until large collections of specimens from every part of the country, 

 and a thorough examination of their structure, satisfied me that we possess not 

 less than six species, belonging to three different genera : one Amyda, one Pla- 

 typeltis, and four Aspidonectes, the geographical distribution of which is jjarticu- 

 larly interesting. In the North-Western States, two species occur together, belong- 

 ing to two different genera, Amyda mutica and Aspidonectes s^jinifer; in the 

 Middle Western States one species, Aspidonectes nuchalis ; in the South-Eastern 



p. 71.) Many similar examples miglit be quoted It is less so in Aspidonectes spinifer, as the figure of 



among the Rodentia. LeSueur published in the Mem. du Mas., Vol. 1.5, PI. 



' The figure of Dr. Holbrook, in the North Amer- 6, distinctly shows. These two figures will at once 



ican Ilerpetology, Vol. 2, PI. 1, represents very dis- exhibit the differences characteristic of the forms of 



tinctly this oblong form of the male Platypeltis ferox. the two species. 



