1864. ] DR. J. E. GRAY ON THE TRIONYCHID2. 89 
stated, but it is probably from the Indian or Australian Seas. It is 
very like the skull of 7'yrse nilotica ; and if it came from Africa, it 
may probably belong to that species. It is described in detail by 
Professor Owen in the Catalogue of the Osteological Specimens in 
that Museum (see p. 181, nos. 922, 923). 
In the ‘Knowsley Menagerie’ I described a species of Trionya 
living in Knowsley Park, which was said to have been sent from Sierra 
Leone, under the name of Tyrse argus, Gray, Cat. Tort. B.M. 48; 
Knowsley Menagerie, t. ; Trionyx argus, Gray, Cat. Shield Rept. 
B.M. 68. When I compare this specimen with the specimen of 
Trionyx spiniferus which I have received from North America, I am 
very doubtful whether there must not have been some confusion 
about the habitat of the specimen, and whether it is not more pro- 
bably a North American species—especially as since our increased 
intercourse with West Africa we have not received any more speci- 
mens. 
The head of the specimen figured in the ‘ Knowsley Menagerie,’ 
which is now in the British Museum, has the nose elongate-conical ; 
and the forehead, as shown in the dry specimen, is elongated, lo- 
zenge-shaped, much longer than broad. 
B. Skull oblong, thin; nose very short ; eyes anterior ; forehead 
elongate, longer than the face; palate flat, with a scarcely 
raised alveolar edge, and only a very slight depression before 
and behind the internal nostrils. 
a. Skull short and broad, much depressed ; alveolar edge of both 
jaws flat, simple. 
PELOCHELYS. 
Head depressed, moderate-sized ; the face very short, shelving ; 
eyes rather close together, superior ; the forehead flat, rather concave ; 
skull much depressed, broad ; nose very short, shelving ; orbits very 
large, subanterior ; forehead depressed, rather concave ; prefrontal 
bones large ; preemaxillary bones none; the maxillar bone circum- 
scribing the lower edge of the exterior nostrils. Palate nearly flat, 
very broad, rather convex in the centre behind, slightly concave (but 
without any central groove) in front of the internal nostrils. Inter- 
nal nostrils oblique, oblong, with a rather wide, deep, short groove 
behind each of them. The alveolar edge flat, simple, with an acute 
scarcely raised edge. Lower jaw very slender, weak, with a simple 
sharp edge, with a slightly thickened internal rib. The first verte- 
bral plate of the shield as broad as the front edge of the second one. 
Professor Owen, in the account of the skull of this genus which is 
in the College of Surgeons, named T’rionyx bibroni, no. 954, describes 
the difference between it and the skull of Trionyz gangeticus, and a 
Tyrse allied to T. nilotica, and he also describes some peculiarities 
in the formation of the dorsal disk (see Cat. Osteol. Spec. Mus. Coll. 
Surg. p. 185, nos, 954-959). 
