Chap. III. GENERA OF TRIONYCIIID.E. 399 



mouth with a sharp l)ill, and with two long surfaces under the nose, which are 

 brought close together when the mouth is shut. The food found in the stomach 

 of a specimen of Amyda mutica, examined in a fresh state, consisted of larvae of 

 Nevropterous insects. 



The type of the genus Amyda is LeSueur's Trionyx muticus. It is thus far 

 the only species known to belong to this genus, unless Trionyx euphraticus, Gcoffr., 

 be generically identical with it, which I have no means of ascertaining. 



Amvda jiutica. Fib. The description of this species by LeSueur is the fullest 

 and most accurate.^ He has distinctly pointed out its most prominent specific 

 peculiarities : the depression along the middle line of the back, instead of an obtuse 

 keel, the total absence of spines along the anterior margin of the carapace and 

 of tubercles upon the back, and the peculiar coloration of the lower surface, which 

 is whitish, without spots or mottled marks, as occur under the neck and upon the 

 lower surface of the feet of Tr. spinifer, Avith which it has often been confounded. 

 LeSueur also mentions the long, narrow, and pointed jaws, which constitute one 

 of its generic peculiarities. The form of the nostrils, first noticed by Dr. Hol- 

 brook, is also generic. 



I have seen more than twenty specimens of both sexes, in every stage of 

 growth.' The males have always a longer tail than the females, extending 

 beyond the margin of the disc, while it is concealed under it, in the other sex. 

 The young, (PI. 6, fig. G and 7,) at the time of hatching, and for some time 

 afterwards, are entirely white below, even under the neck and upon the lower 

 sui'face of the feet ; the latter, however, becomes bluish gray with age, but it 

 is never spotted or mottled. Upon the sides of the head, from the eyes back- 

 wards, runs a narrow white band bordered by black lines, which is merged behind 

 in the white surfiice of the lower side of the neck, but extends forwards across 

 the eye to the tip of the proboscis. This band disappears more or less in old 

 specimens. In very young specimens, the back has slight black spots upon an 

 olive colored ground, and exhibits, along the hind margin and the sides of the 

 carapace, a broad yellowish band circumscribed by a black line. With advancing 

 age the marginal band disappears, and the dark marks upon the back spread 

 mitil they vanish entirely, and the ground becomes itself darker and more gray- 



' In Mem. Mus. Hist. Nat. Paris, 1827, vol. 1.'), York, vol. 3, p. 7, PI. C, fig. 11) represents it .-is the 



p. 263, PI. 7. It has since been described by Major young of Tr. ferox, though he considered it at first 



LeConte, (Lye. Nat. Hist. New York, vol. 3, p. 95,) as a distinct species, for which bo b:ul proposed the 



and by Dr. Ilolbrook, (N. Aincr. Ilorp. vol. 2, p. 11), name of Tr. occUatus.- His figure loaves no doubt 



PI. 2.) J. E. Gray considers it and Tr. ferox as that he had a specimen of Tr. muticus before him. 



being the only genuine representatives of the genus "Wagler refers it to his genus Aspidonectes, and Du- 



Trionyx, as he wuiild limit it. Delvay (Zool. of New meril and Bibroii to ilair genus Gymnopus. 



