CONCHOLOGY. 59 



C. tuberculatum. The tuberculated Cardium. 

 Species not gaping, with large ribs armed with nodules. 



2. Cardita. Twenty-one species. 

 Lamarck took this genus from the Chama on account of 

 several peculiarities in the shell as well as in the animal. It 

 is not affixed to other bodies by its lower valve, but, accord- 

 ing to De Blainville, lies exposed on the rocks. There is 

 some difficulty in distinguishing this genus from the Veneri- 

 cardia, without carefully examining the position of the two 

 teeth- 

 Shell regular, thick, solid, equivalve, more or less inequi- 

 lateral ; summit dorsal, always very recurved anteriorly ; 

 hinge similar, formed by two oblique teeth ; one short cardi- 

 nal placed beneath the umbo, the other oblique, arched, mar- 

 ginal, and prolonged ; ligament elongated, sub-exterior, and 

 inserted ; two very distinct muscular impressions. 



Cardita sulcata. Cardita intermedia. 



C. ajar. C. trepezia. 



C, turgida. C. bicolor. 



C. squamosa. C. depressa. 



C. phrenetica. C. concamerata. 



C. crassicosta. C. sinuata. 



C. rufescens. C. aviculina. 



C. calyculata. C. citrina. 



C. subaspera. C. sublaevigata. 



C. nodulosa. C. corbularis. 

 • C. lithophagella. 



C. crassicosta. The thick-ribbed Cardita. 

 Species elongated, a little gaping at the inferior margin ; 

 ligament concealed. 



C. sulcata. The furrowed Cardita. PI. 10, fig. 3. 



Sub-cordiform or oval, more transverse than longitudinal ; 

 colour white, tesselated with brown ; posterior depression 

 heart-shaped ; longitudinal, convex, transversely-striated ribs. 



