190 , THE BERMUDA ISLANDS. 



posterior flattened. Right valve with widely diverging car- 

 dinal teeth, the space between which receives the double-tooth 

 (grooved medially) of the left valve; lateral teeth in right 

 valve. 



Pallial sinus large, extending more than half across the 

 shell ; external surface (white) concentrically and delicately 

 lined by the lines of growth. 



Length of shell three-quarters of an inch ; height, two- 

 thirds of an inch. 



Mysia pellucida. PI. 17, fig. 3. 



Shell thin, convex, ovally orbicular; the umbones mod- 

 erately prominent; no lunule ; hinge-line linear, a single 

 medially-grooved cardinal tooth in the left valve (resembling 

 Felania). 



Adductor impressions oval, not much elongated. Shell 

 white, nearly smooth. 



Length of single specimen somewhat over a half-inch; 

 height the same. 



Cytherea Penistoni, PI. 17, fig. 4. 



Shell sub-trigonal, the beaks prominently elevated ; lunule 

 cordiform ; the dental characters normally those of the genus ; 

 anterior lateral tooth (left valve) triangular, lamellar. 



Margin of shell even ; pallial sinus broad, directed upwards, 

 and not quite reaching the centre of the shell. Lines of growth 

 closely set, and even. Shell covered with a chestnut epidermis ; 

 interior purplish. 



Length, .6 inch ; height, .5 inch. 



It gives me pleasure to name this delicate, and abundantly 

 represented, Cytherea after my friend Miss. A. Peniston, of 

 Peniston's, from whom I have received much valuable assistance 

 in the preparation of my material illustrating the Bermudian 

 fauna. 



