_Shell._ Solid, thick, regular, perfectly equivalved and close, more or less inequilateral; summits well marked and inclined to the front; hinge subsimilar; the middle cardinal tooth forked, or three cardinal teeth more or less contiguous and convergent towards the summits; ligament thick, often arcuated, convex, exterior; two distant muscular impressions; cordiform depressions beneath the beaks. Inhabits the British and American seas. One hundred living species. Nine fossil. Venus reticulata. V. rugosa. V. corbis. V. crebiscula. V. discina. V. cancellata. V. marica. V. sulcaria. V. cardivides. V. texturata. V. elliptica. V. rariflamma. V. mercenaria. V. pullastra. V. gallina. V. truncata. V. pectinula. V. anomala. V. lamellata. V. exilis. V. rufa. V. Scotica. V. hiantina. V. virginea. V. corugata. V. ovulæa. V. papilionacea. V. callipyga. V. punctifera V. nebulosa V. literata Venus floridella. V. aphrodina. V. pulchella. V. aphrodinoides. V. tristis. V. flammea. V. puerpera. V. verrucosa. V. pygmæa. V. casina. V. crenulata. V. plicata. V. granulata. V. pectorina. V. cingulata. V. textilis. V. grisea. V. geographica. V. Dombeii. V. decussata. V. lagopus. V. glandina. V. gallinula. V. retifera. V. sulcata. V. galactites. V. exalbida. V. scalarina. V. dorsata. V. aurea. V. crassisulca. V. carneola. V. petalina. V. cornularis. V. adspersa. V. opima. V. turgida. V. flammiculata. V. strigosa. V. Perronii. V. elegantina. V. undulosa. V. vermiculosa. V. vulvina. V. marmorata. V. Malabarica. V. laterisulca. V. subrostrata. V. phaseolina. V. Florida. V. bicolor. V. catenifera. V. sinuosa. V. rimularis. V. ovata. V. pumila. V. inquinata. · · · · · V. notata.* V. præparea.* V. elevata.* V. inequalis.* V. castanea.* V. Nuttallii* V. staminea.* V. Californica.* V. lamellifera.* V. Mortoni.* 4. Genus _Venericardia_. Pl. VII. _Animal._ Nearly as above. _Shell._ Suborbicular, inequilateral, equivalve, sides having usually longitudinally rayed ribs; hinge with two oblique cardinal teeth in each valve, turned in the same direction. Five living species. Ten fossil species. Venericardia Australis. V. imbricata. V. flammea. V. Tankervillii. V. crassicosta. CONCHÆ FLUVIATILES. Three Genera. 5. Genus _Cyclas_. Pl. VII. _Animal._ Body oval, thick; edges of the mantle simple; tubes short and united; foot wide, compressed at base, and terminated by a sort of leg or appendage. The shells of this genus are very small, found buried in the mud of fresh waters; summits never eroded, but some species are so thin as to be transparent.