CONCHIFERA. 



269 



an interlacing, from the intestines ; on each side are two 

 leaf-shaped gills, the inner one is united with the outer in 

 the front, behind, the two inner gills are united ; the lip 

 tentacles are rather long. — 2 species ; also fossil. 

 The living species are found in the Mediterranean. 



Thyasira. Leach. (Axinus Sow. ; Cryptoton Tur- 

 ton ; Pty china Phil.) — Shell free, equivalve, transverse; 

 anterior side short; posterior side produced, truncated, 

 with a lunette near the bosses ; hinge having a long 

 oblique ligament placed in a furrow. Animal unknown. 

 — 2 species ; also fossil. 



Found in the Northern Sea and the Mediterranean. 



Chironia. Desh. — Shell regular, equivalve, thin, with 

 an epidermis ; the hinge narrow, on the right side of which 

 is a curved tooth, directly under the boss, and an oblique 

 hinder lateral tooth ; in the left valve are two similar 

 teeth, but smaller; a short, very broad inner ligament 

 between the teeth of the hinge, resting on small oblique, 

 spoon-shaped processes, which are entirely hid under the 

 bosses ; two muscular and one pallial impression. Animal 

 unknown. — 1 species. 



Found on the German shores. 



Kellia. Turton. (Erycina Payr. not Lam ; Bornia 

 Phil. ; Pythina Hinds.) — Shell thin, equi- 

 valve, subequilateral, suborbicular, tumid 

 or compressed, closed, smooth or concen- 

 trically striated; beaks incurved, small, 

 inner margin smooth; hinge composed of 

 one or two primary teeth in either, and 

 a lateral one in both valves ; ligament internal, or sub- 

 marginal, in some species placed in a cartilage-bed, 

 formed of the thickened hinge margins of each valve 



