CONCHIFERA. 



which gives that valve the appearance of having an indistinct 

 or obscure cardinal tooth. 



Distribution, 4 species. Europe. 



Fossil, Tertiary. Two of the three British species occur in a 

 fossil state in the Coralline Crag. 



Spoetella, Deshayes (see p. 457). 



Example, Psammotea dubia, Defrance. 



Shell oblong, smooth, depressed, sub-equilateral; valves 

 closed. Hinge narrow, with two unequal, diverging teeth in 

 the left<valve, one in the other ; the lateral teeth are wanting. 

 Muscular scars large, oval, nearly equal ; pallial line simple. 

 Ligament external. 



Fossil, 17 species. Tertiary. Paris basin. 



Possibly some of the Liassic species referred to Unicardium 

 belong to this genus. 



CoRBiCELLA, Morris and Lycett, 1853. 



Etymdlogy , diminutive of Corhis, 



Type, C. subsequilatera, Lycett. 



Shell destitute of ornament, ovately elongated, rather com- 

 pressed ; anterior side small ; hinge characters differ from those 

 of Corhis, in the absence of the anterior lateral tooth, and in 

 the oblique internal ridge passing downwards behind the ante- 

 rior muscular scar. 



Corhicella is intermediate between Corhis and Tancredia; and 

 from the latter, to which it is more nearly allied, it is separated 

 by its more ovate form, and by the absence of the posterior 

 oblique angle, and in the possession of a lengthened hinge- 

 lamina and depressed remote posterior lateral tooth. 



Fossil, 7 species. Upper part of Liferior Oolite — Oxfordian. 

 England; Prance. 



[PAMILT EJELLIID^.] 



Las^a, Brown, 1827. 



Etymology, possibly a corrupt derivation of Xaicnji'iov, a shield. 



Type, Cardium rubrum, Montagu. 



SynonymSy Poronia, Eecluz; Cylcadina, pars; Kellia, pars; 

 Bornia, pars. 



Animal with the mantle folded on the anterior side so as to 

 form a wide but incomplete incurrent tube ; the excurrent tube 

 is inconspicuous, placed on the opposite side ; foot long. 



B 73 



