226 



Zoological Society : — 



hood of the four larger scuta bear a projecting ohlong umbo ; and 

 C. frontatus has this developed in a manner still more marked. 



Fig. II. 



Fig. 12. 





n"* 



The same character prevails in the rest of the scuta. In all three 

 species there are six rows of large scuta down the back, varying in 

 width, diminishing to four rows in the lumbar region. In C. vulgaris 

 these scuta are flat, with only a slightly raised longitudinal line or 

 carina. In C. leptorhynchus this carina is much more raised, so as to 

 form regular crests. In C. frontatus some of them have an oblong 

 umbo, others a crest, and others only a raised line : the affinity in 

 this respect is greater with C leptorhynchus than C. vulgaris. It is 

 the same with regard to the crest down the tail. In all three the 

 rows of dorsal scuta down the back become only four in number 

 after passing the hind legs, forming four raised lines, two on each 

 side of the spine ; the inner crests or lines on each side then gra- 

 dually approximate (in C. vulgaris forming a narrow channel) and 

 thin off and become obliterated. The outer crest on each side, at 

 about the seventh or eighth joint behind the hind legs, becomes 

 broader and spreads out into a flat plate or leaf turned out horizon- 

 tally on each side. There are about seven joints in which this flat 

 table-shaped position of the scuta occurs, and about the same number 

 prevails in all three. As this disposition, however, does not com- 

 mence suddenly at any particular joint, but proceeds by gradations 

 out of the crest on the back, the number may be modified according 

 to the degree at which the observer reckons the horizontal leaf to 

 commence. The size of these scuta is proportionally larger in C. 

 frontatus and C. leptorhynchus than in C. vulgaris. These hori- 

 zontal thin scuta extend one on each side for a certain distance ; and 

 then all at once the double row ceases, and is replaced by a series of 

 single erect scuta running down the top of the tail. In my specimens 

 the number of joints before this single crest commences, reckoning 

 from immediately behind the hind legs, is as follows : — 



C. vulgaris 18 



C. leptorhynchus 17 



C. frontatus 13 



