14 



are rounded, and composed of a number of round obtuse 

 tubercles. These seven ridges are equidistant, and consist 

 of one along the median line of the back, one on each 

 margin of the shell, and two on each side between the 

 dorsal and the marginal one. The anterior paddles are 

 remarkably long, being more than twice the length of the 

 hinder ones, and somewhat falcate ; the latter, however, 

 are generally broader than the former. They are covered 

 with a perfectly smooth skin. The tail is acute, much 

 compressed at the sides, and extends only to the extreme 

 point of the dorsal shell. The following figures of these 

 parts are from the specimen above mentioned. 



The young individual differs from the adult more con- 

 siderably in this species than in any other species of the 

 order with which I am acquainted. Some of the peculiari- 

 ties of the former age have already been alluded to ; in 

 addition to which may be mentioned the more full and 

 rounded form, the larger head, the larger and more ex- 

 panded eye, and the existence of five ridges on the ster- 

 num. The eye opens almost vertically, which gives a 



