1864.] DR. J. E. GRAY ON THE TRIONYCHID&. 97 
Cryptopus senegalensis, Dum. et Bib. Erp. Gén. ii. 504; Gray, 
P. Z.S. 1860, p. 316. 
Hab. W. Africa: River Gambia. 
The young specimens in the British Museum from the River Gam- 
bia have the head pale grey, with some pale roundish spots (and 
without any indication of black streaks). 
The specimen of Emyda senegalensis which we have received from 
Paris, as coming from Senegal, is evidently the young of a Cycla- 
nosteus, and not of an Emyda; and as it agrees in many particulars 
with the young specimen which we have received from the Gambia 
as Cyclanosteus petersit, it is most probably the young of that spe- 
cies. It differs from the specimen which we have from the Gambia, 
of the same size, in having a few scattered black specks on the hinder 
part of the dorsal shield; but this probably arises from the Senegal 
specimen having been better preserved by being placed and kept in 
stronger spirits. 
In the British Museum there is a skull (figs. 19, 20, 21) which was 
received from the River Gambia without the animal, and which appears 
to be that of the adult Cyclanosteus senegalensis. The whole upper 
edge of the lower jaw is very much dilated and moderately concave ; 
while in the skull of a half-grown specimen, apparently of the same 
species, the front half of the lower jaw is high, narrow, with a 
simple sharp edge, and the hinder portion of the upper edge is more 
and more dilated and flattened as it approaches the condyle, so 
as to form an oblong, concave, flattened disk on the surface. Un- 
fortunately I have not the skull of a young specimen to compare 
with the other two; but I should not be surprised to find that the 
whole upper edge in the young specimen is simple and shelving, like 
the adult state of Tyrse nilotica. 
I may observe that I have not seen any observations in Professor 
Agassiz’s work which show that he has observed such a change of 
form of the lower jaw in any of the North American species of this 
family. In his account of the general characters of the family he 
simply observes, “ the lower jaw grows more flattened towards the 
front end.” (Contrib. i. 332.) 
c. The margin of the dorsal disk strengthened with a series of in- 
ternal marginal bones ; skull oblong, swollen, convex. Emydina. 
Emypa. 
Emyda, Gray, Syn. 1831 ; Cat. Shield Rept. 63. 
Trionyx, Wagler, 1830. 
Cryptopus, Dum. et Bib. 1835. 
The face short, convex ; forehead and crown flattened above. 
The skull, as figured by Wagler (N. Syst. Amphib. t. 2. f. 24-31), 
has a high arched nose, rather flattened over the eyes, and a flat fore- 
head. The palate with a narrow groove, rather narrowed in front of 
the oblong internal nostril, placed in front of the middle of the alveo- 
lar margin. The alveolar margin of the upper jaw is flat, rather 
Proc. Zoou. Soc.—1864, No. VII. 
