214 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIATA. 



somewliat oblique, convex, T\'itli twenty-four little ele- 

 vated, convex, smootliish ribs, marked toward the mar- 

 gins with transverse lamellae, becoming elevated into 

 triangular spines at the posterior end, where the inter- 

 stices are granulate. Exiguus, very diminutive. 



5. Cardium Icevigdtum. — Shell roundish-oval, much 

 produced behind, moderately convex, Avith a yellowish 

 epidermis, and very numerous obsolete ribs. Lcevigdtus, 

 smoothed. 



6. Cdrdiinn elongdtum. — Shell ovato-orbicular, some- 

 what oblique, compressed, with the dorsal margin nearly 

 straight, and about twenty-six convex, echinate ribs. 

 Elongdfus, lengthened. 



Gexus 2. DoxAx. — Shell subtriangular, compressed, 

 very inequilateral ; the posterior end shorter and angu- 

 late ; umbones small ; two small divergent central teeth 

 in both valves. Dunax, a kind of shell. Linnaeus. 



1. Bonax truncidus. — Shell oblong, anteriorly pro- 

 longed and rounded, posteriorly angulate, smooth, with 

 faint divergent striae. Tn'mculus, cut short. 



2. Donax denticiddtus. — Shell crenato- triangular, 

 anteriorly prolonged and semioblong, posteriorly angu- 

 late, glossy, with fine radiating striae, which are punc- 

 tured or transversely grooved. Named from the denti- 

 culated or crenated margin. 



Family VIII. — Tellixixa. 



Animal orbicular, roundish, or oblong, compressed, 

 with the mantle open anteriorly for the foot, and bordered 

 with tentacular appendages, closed behind, but \\ith an 

 aperture for the elongated and separated siphons ; foot 

 much compressed, sharp-edged ; shell orbicular, roundish, 

 or oblong, inequivalve, inequilateral, the posterior end 

 shorter, and llexuous ; hinge with one or two small 

 central teeth. Named from the genus Tclhna. 



Gexus 1. Kellia. — Shell roundish or oval, equivalve, 

 convex, closed, concentrically striate ; umbones rather 

 large ; hinge with two central teeth in one valve, a tooth 



