424 DR. J. E. GRAY ON CYCLANOSTEUS. [May 9, 
on the middle of the outer side of the left; a rugose callosity, of 
a triangular shape, on the outer side of the right callosity of the 
second pair; the space between the outer hinder angle of the second 
pair of gular callosities, the side of the odd third plate, and the front 
edge of the middle of the abdominal callosity is filled up with an 
additional callosity ; on the left side this callosity is single and of 
a square form; on the right side it is divided into two parts, the 
anterior part being triangular, and the hinder rather irregular in its 
outline (see fig. 1). 
The middle lateral abdominal callosity of this specimen is large ; 
but these callosities differ greatly in size and form in the different 
specimens. This specimen seems to show the callosities in the 
maximum state of development ; and if I had not possessed a series 
of specimens apparently coming from the same locality, showing 
how mutable the form and size of the callosities are in this species, 
I should have been induced to believe it exhibited the characters of 
a distinct and well-marked species. 
As in all other Trionychide, the young specimen of this species 
is destitute of any callosities; but, from the foregoing observations, 
the gular and abdominal callosities appear to be developed nearly at 
the same time; and the hinder pair do not make their appearance 
till later in the life of the animal, and seem to be gradually deve- 
loped, being at first small and roundish, until they cover the whole 
length of the bone on which they are placed; hence they vary con- 
siderably in shape and size in the different individuals of the species. 
The Tortoises under examination may be referred to three prin- 
cipal varieties :— 
