107 



Figure. 



Tapes textilis. PL 35. Fig. 193. Shell of an usually smooth species, 

 showing the hinge of three close cardinal teeth, destitute of lateral 

 teeth. 



Genus 2. CYTHEILEA, Lamarck. 



Animal ; oblong, with its mantle freely open, and plain at the 

 margins ; foot large, linguiform, not furnished with a byssal 

 groove ; siphons united nearly to their extremities ; orifices of 

 both with simple cirrhi. (Forbes.) 



Shell ; obliquely subtriangularly orbicular, mostly smooth and por- 

 cellanous, sometimes concentrically lamellatehj striated, very 

 rarely spined around the posterior ; hinge composed of three di- 

 varicate cardinal teeth in one valve, interlocking with four in 

 the other, the outer one of which diverges more or less into the 

 form of a lateral tooth. 



Of this genus we have a grand typical example on our own shores in C. 

 Chione, and it is the only Cythercea, out of a hundred and sixty-four, that 

 inhabits Britain, excepting a small one of the subdivision Circe. The ani- 

 mal has no byssal groove in the foot, as in Tapes, and the cirrhi of both 

 orifices of the siphons are simple. Three well-marked groups are indicated 

 by the following : — C. Chione, of which type the species are far the most 

 numerous, is the representative of a series with shells of large size and 

 porcellanous surface, sometimes concentrically grooved, but not otherwise 

 sculptured, richly banded, rayed, or spotted with brown, rust-brown, and 

 purple-brown, and sometimes blue. C. Blone represents a type much more 

 limited in species, of which the shell is smaller and densely concentrically 

 lamellately ridged. The spines which are so remarkable a feature in C. 

 Blone do not belong to the group, but only to two other species, C. Uri- 

 naria and multisplnosa, and it is even doubtful whether all three are not 

 varieties of one and the same species. C. scrlpta (Bonax scrlpta, Lamarck), 

 with a flat wedge-shaped shell, represents another group, of which there 

 are only seven species ; and fifteen species have been separated under the 

 name of Circe, with a stout squarely orbicular pinched shell, whose animal 

 varies in having the margins of the siphonal orifices fringed, and is more 

 allied in this respect to Cyprlna. 



