CYCLADID^ 7 



Tribe VI. — CyclostomidIvE. 



Animal — With a spiral body; two tentaculce with eyes (it their 

 inner bases; foot ovate. Terrestrial. 



Shell — Ovate and turreted, strong; mouth oval; operculum 

 consisting of several whorls. It includes, according to 

 the present arrangement, two genera — Cyclostoma and 

 Acme. 



CYCLADIDiE. 



Cyclas. Brugiere. 



Shell — Subglohose, equivalved, more or less finely stri- 

 ated ; cardinal teeth small, sometimes undis- 

 tinguishable, one in the right and two in the left 

 valve. Lateral teeth developed transversely , dis- 

 tinguished from the Pisidia by being larger, 

 rounder, and more equilateral. 



Animal — Mantle produced behind forming a siphon, 

 which is divided into two nearly equal tubes. 



C. RivicoLA. Leach. PL I, fig. 2. 



Shell subglohose, striated concentrically ; umbones obtuse; cardmal 

 ligaments distinct. 



Tellina cornea ; var. B. Linn. Cyclas cornea, Drap. 



This is the largest of British Cycladidse. Its form is 

 roundish, oval, and very slightly inequilateral. It is 

 comparatively strong and opaque. The valves are 

 covered more or less closely with concentric striae, 

 which are less distinct on the umbones. The epidermis 

 is glossy and of a brownish green, with darker zones ; 

 the umbones have generally a yellow tinge. Interior 

 of a bluish white colour. 



Ordinary length five-sixths of an inch, and breadth 

 two -thirds of an inch. 



The tubes of the animal slightly tinged with brown, 

 foot and mantle white. 



Hab. The river Thames in considerable abundance; 

 it has also been found in the Trent, New River, Lea, 



