CRYPTOCHITON. 479 



petasus, Adams and Eeeve. vespertina, Gould. 



Simpsonii, Gray. 



Genus KATHARINA, Gray. 



Mantle-margin horny, smooth. 



Shell with the valves deeply immersed in, and partly 

 covered by, the mantle, the exposed parts small, cordate, 

 as broad as long; the hinder valve with the apex sub- 

 central. 



Ea^. K. tunicata, JVuod, pi. 54, fig. 8. 



In this genus the lamina of insertion is greatly pro- 

 duced, that of the anterior valve nine-lobed, that of the 

 posterior four-lobed, and that of the middle bi-lobate. The 

 margins of insertion are nearly as in Mopalia, but the 

 valves are more covered, and the mantle-margin is bare 

 and horny. 



Species of Katharina. 



Douglasiae, Graij. tunicata, Wood. 



submarmorea, Mldd. 



Genus CRYPTOCHITON, Gray. 



Mantle with tufts of spicula ; gill extending all round. 



Shell with the valves internal, entirely concealed by the 

 mantle ; umbo of growth of all the valves central. 



JE.v. C. Stelleri, Middendorff, pi. 55, fig. 1, 1, «. 



In this genus the beak of all the valves is central, and 

 the shell is quite internal, being entirely enclosed on 

 every side by the mantle, which covers the body like a 

 capsule ; the epidermis is somewhat pustulose,the pustules 



