154 



SECTION III. CONCIIIFERA LAMELLIPEDA. 



This section is divided into five families, viz. Conchse, Cardiacea, Arcacea, 

 Trigoniana, and Naiada. 



CONCHiE.— Seven Genera. 



Three cardinal teeth at least in one valve, with as many, or less in the 

 other; sometimes with lateral teeth. 



The Concha? are divided into Fluviatiles and Marina?. 



CONCHA FLUVIATILES. 



Cyclas. Shell ovate-globose, transverse, equivalve, the beaks tumid; 

 cardinal teeth very small, sometimes scarcely perceptible; occasionally two 

 in each valve, one of them plaited in two; sometimes only one plaited or 

 lobed tooth in one valve, and two in the other; lateral teeth transversely elon- 

 gated, compressed, lamellar. Ligament external. 



C. rivicola, C. obliqua, C. fontinalis, C. striatina, 



' cornea, ' calyculata, ' australis, ' Saratogea. 



c lacustris, ' obtusalis, ' sulcata, 



Cyrena. Shell rounded, triangular, turgid or ventricose, inequilateral, 

 solid, covered with an epidermis; the beaks eroded; hinge having three teeth 

 in each valve. The lateral teeth are nearly always two in number; one of 

 them often near the cardinal. Ligament external, inserted in the largest side. 



C. trigonella, C. fuscata, C. depressa, C. Caroliniensis, 



• orientalis, ' fluminea, ' Bengalensis, 1 fossil species. 



* cor, ' violacea, ' Zeylanica, 



Galathea. Shell equivalve, sub-triangular, covered with a greenish epi- 

 dermis; cardinal teeth sulcated; two in the right valve, approaching at their 

 base; three in the other, the middle one advanced, and separate; lateral teeth 

 distant. Ligament external, short, protruding, turgid, nymphse prominent. 



G. radiata. 



CONCHA MARINE. 



Mostly no lateral teeth ; the whole shell frequently covered with an epidermis exeept 

 at the beaks. 



Cyprina. Shell equivalve, inequilateral, obliquely cordate, the beaks 

 obliquely curved; three unequal, cardinal teeth, approximating at their base, 



