CONCHACEA. Bl. The eighth family of the order Lamellibranchiata, Bl. The shells are described as follows: nearly always regular, valves closed all round; apices curved towards the anterior; dorsal hinge complete, with teeth and ligament; the latter external or internal, short and thick; two distinct muscular impressions, united at the lower part by a parallel impression, which is frequently sinuated at the posterior. The genera described in this family are divided into three sections. First, those which are regular, and have distant lateral teeth, Cardium, Donax, Tellina, Lucina, Cyclas, Cyprina, Mactra, and Erycina. Second, those which are regular, and have no distant lateral teeth, Crassatella and Venus. Third, those which are irregular, Venerupis, Coralliophaga, Clotho, Corbula, Sphænia, and Ungulina. CONCHACEA. Lam. A family of Lamarck's order Conchifera Dimyaria. Regular, unattached in general, closed at the sides. They are always more or less inequilateral. The _Marine_ Conchacea are those which inhabit the sea. The fluviatile Conchacea are those which are found in rivers, ponds, &c. Each of these contain various genera, which may be arranged as follows:-- _Fluviatile._ 1. CYRENELLA. Three cardinal teeth; ligament long; shell thin. Fig. 114. 2. CYCLAS. Thin, oval; cardinal and lateral teeth; anterior side shortest, including _Pera_. 3. PISIDIUM. The same, with the posterior side shortest. Fig. 112. 4. CYRENA. Thick; cardinal and lateral teeth. Fig. 113. 5. POTAMOPHILA. Two thick cardinal teeth. Fig 115. _Marine._ 1. CYPRINA. Two cardinal teeth, and one remote lateral tooth. Fig. 116. 2. VENUS. Three cardinal, no lateral teeth; including _Artemis_. Fig. 118, 119, 119a. 3. CYTHEREA. Several cardinal teeth; one very short lateral tooth. Fig. 117, 117_a_, 117_b_, 117_c_, 117d. 4. PULLASTRA. Cardinal teeth notched, otherwise like Venus. Fig. 120. 5. ASTARTE. Three cardinal teeth; ligament short. Fig. 110. VENERICARDIA belongs to the Cardiacea. CONCHIFERA. Lam. The 11th class of Invertebrata, consisting of all those animals which have bivalve shells. Lamarck divides the class into Dimyaria, which have two adductor muscles; and Monomyaria, which have but one.