22 



CHELYDRID-E. 



halfgrown, becoming gradually smoother with age. Vertebral 

 shields much broader than long, at least three fourths the width of 

 the costals. Plastron with angular lobes ; bridge very narrow, 

 somewhat variable in width, but never more than one tenth of the 

 length of the plastron *; the hypoplastral bones enter for a much 

 greater part in the formation of the bridge than the hyoplastra, the 

 outer, digitate portion of which is scarcely expanded. A series of 

 two or three iuframarginals separates the marginals from the abdo- 

 minal, the transverse diameter of which equals at least twice the 



Fig. 4. 



Shell of Chclydra serpentina. 



longitudinal. Snout short and pointed ; interorbital space narrow. 

 Skin very warty ; a pair of very small barbels on the chin. Tail 

 nearly as long as, or longer than, the carapace in the young, two 

 thirds or three fourths that length in the halfgrown and adult ; a 

 strong crest of large compressed tubercles along its upper surface ; 

 a series of large divided scutes along its lowe - surface. 



* From wluit is known )o Ix- t be ease in Stauroti/pux, we may concluflo tlint 

 the sppc'inipns witli hroadcM- hi-idgp are (emales. 



