FAMILY 8. CONCHACEA (MARINA). 89 



Tellina hermaphrodita, Dillwyn. 

 Egeria radiata, Roissy. 

 Megadesma radiatum, Bowditch. 

 Potamophila radiata, Sowerby. 

 Cyclas radiata, De Blainville. 



CONCHACEA MARINA. 



Testa epidermide raro induta ; cardine dente laterali unico instructo, 

 saepe nullo. 



To say that there is no such thing in nature as a true species, but that 

 a species is merely an artificial limit devised by the ingenuity of man to 

 facilitate the systematic arrangement of created things, would be to make 

 an assertion both dangerous and presuming. Yet, when we contemplate 

 the immense series of marine Conchacea ; when we examine the charac- 

 ters by which they have been subdivided, and observe how the relative 

 value of these characters has disappeared through the discovery of the 

 nicest intermediate modifications, we are lost in perplexity, and forced 

 to acknowledge our embarrassment. The animal of the marine Con- 

 chacea is the same throughout, and on reference to its testaceous cover- 

 ing, we are scarcely able to detect any decided change of character. We 

 must therefore trust to our description of the chief typical characters of 

 the genera we have thought it most useful to select. 



The shell of the marine Conchacea differs from that of the fluviatile in 

 being mostly destitute of epidermis, and in having but one lateral tooth, 

 often none ; the cardinal teeth are the same. They are divided into five 

 genera, as follows : 



Cyprina. Cytherea. 



astarte. pljllastra. 



Venus. 



VOL. I. N 



