1865.] DR. J. E. GRAY ON A NEW FORM OF TRIONYCHIDE, 323 
4. Notice or A New GENUS AND SPECIES OF THE FAMILY TRIO- 
NYCHIDZ FROM WESTERN Arrica. By Dr. J. E. Gray, 
F.B.S., F.L.S,,; 27e; aE 
The British Museum has just received two specimens of a Trionyx 
with covered legs from Western Africa (collected by the late Dr. B. 
Baikie, probably on the Niger), which is evidently different in 
structure from any we have before received from that country, and 
which I am inclined to believe is an entirely new form. 
It differs from the other African Trionyches with covered feet in 
only having two pairs of callosities on the sternum; while Hepta- 
thyra has seven, and Cyclanosteus has nine such hardnesses on the 
sternal bones. These callosities differ in disposition and mode of 
development, as well as in manner, in the three genera. The form 
of the skull is like that of the genus Cyclanosteus ; that is to say, 
the face is moderate, with eyes about halfway between the front of 
the zygomatic arch and cavity of the temporal muscle and the end 
of the nose ; but it differs from the skull of the latter genus in the 
forehead and crown being wider and flatter. 
The genus (which I should refer to the tribe Cyclanosteina) may 
be defined thus :— 
TETRATHYRA. 
The face of the skull short, convex, arched in front ; orbits lateral, 
shelving, about midway between the end of the nose and the front 
of the zygomatic arch ; forehead flat, rhombic, broad. The dorsal 
shield with flexible margins, without any marginal bones; front of 
dorsal shield warty above and without any odd nuchal bone. Ster- 
num flat, with broad rounded lobes covering the feet, and two pairs 
of sternal callosities ; the front pair small, rounded, on the front 
ends of each of the front pairs of sternal bones ; the lateral pairs 
are large, oblong, broadly notched out behind, and very rugose. 
This genus differs from Cyclanosteus in the want of any odd bone 
in front of the dorsal shield, as well as in the number and disposition 
of the sternal callosities. 
The upper surface of the front of the disk is closely covered with 
roundish warts. The sternal callosities are not developed in the 
young specimen, the larger lateral pair being first indicated as the 
animal increases in size. The dorsal disk of the young specimen is 
marked with close grains, or warty, in rather arched longitudinal 
ridges. 
There are some young specimens in spirits from West Africa in the 
Museum, which belong to this species; they differ from the young 
of C. senegalensis in being marbled, while that species is marked 
with distinct small subcircular black spots. 
This second genus of Cyclanosteina may explain the reason why 
we have two skulls from West Africa the one with the front and 
the other with the whole upper edge of the lower jaw dilated, as 
figured in the ‘ Proceedings of the Zoological Society’ for 1864, 
fig. 18, p. 95, and fig. 21, p. 96. 
