leptonidjE. 477 



slightly gnping; surface of valves concentrically striated. 

 Hinge composed of two primary teeth in each valve, the 

 anterior lamellar; ligament external; cartilage internal, 

 placed in a triangular pit behind the teeth. Pallia! line 

 simple. 



Syn. Turtonia, Hartley. 



Ex. C. minutum, O. Fabricius, pi. 114, fig. 11. Shell, 

 C. antarcticum, Philippi, fig. 11, a, 11, b. 



The great peculiarity of Cyamium is in the produced 

 anal siphon of the animal. In C. minuta the longer side 

 of the shell is posterior, while in Kellia the shorter side is 

 posterior. 



Species of Cyamium. 



antarcticum, Phil. elevatum, Stimp. 



minutum, 0. Fahr. 



Fam. LEPTONIDiE. 



Animal compressed. Mantle freely open in front, its 

 margin extending considerably beyond the shell, and bear- 

 ing, superiorly, a range of filaments, one of which is much 

 larger than the rest ; a short siphonal tube, with a single 

 aperture, at the larger end of the shell ; branchial leaflets 

 two on each side, and separate. Foot thick and tapering, 

 keeled and disked, furnished with a byssal groove. 



Genus LEPTON, Turton. 



Shell equivalve, orbicular, sub-equilateral, compressed, 

 gaping slightly at the sides ; surface of valves shagreened, or 

 smooth ; margins plain ; beaks acute. Hinge composed of 

 a pair of teeth-like lamina? on each side of a triangular, 



vol. it. 3 Q 



