CUCUMIS. Klein. MARGINELLA, Auct. CULTELLUS. Species of LUTRARIA, Lam. which have the umbones placed near the extremity of the shell. _Ex._ L. Solenoides, fig. 78. CUMA. Humph. FUSUS and FASCIOLARIA, Lam. CUMINGIA. Sow. _Fam._ Mactracea, Lam.--_Descr._ Equivalve, inequilateral, transverse, rounded anteriorly, subrostrated posteriorly. Hinge with a central spoon-shaped cavity in each valve, containing the cartilage; a very small anterior cardinal tooth in each valve; two lateral teeth in one valve, none in the other: muscular impressions two in each valve, distant; palleal impression with a very large posterior sinus.--_Obs._ The species known at present are found in sand, in the fissures of rocks in Tropical climates. They resemble Erycina in general form and character, but differ in having the internal cartilage placed in a prominent spoon-shaped process, while that of Erycina is contained in a hollow which sinks under the umbones. This genus should be placed near Amphidesma. Cumingia mutica, fig. 87. CUNEIFORM. (_Cuneus_, a wedge.) Wedge-shaped, as Donax, fig. 108. CUNEUS. Megerle. VENUS Meroe, Linn. and similar species. CUNICULA. Sw. A sub-genus of Uniones, thus described:--"Ovate, oblong; bosses thick, but depressed; cardinal teeth moderate. C. planulata, patula, rubiginosa, secura, purpurascens." CURVED. Arched or bent. _Ex._ Dentalium, fig. 2. CURVULA. Rafinesque. A fossil imperfectly described as differing from Pinna, in being inequivalve. CUVIERIA. Ranz. (Baron Cuvier.) _Class_, Pteropoda, Lam.--_Descr._ Thin, transparent, glassy, cylindrical, rounded and inflated at the closed extremity, compressed towards the opening, so as to render it oval. This genus differs from Vaginula in being rounded, instead of pointed, at the lower extremity. Mediterranean. Fig. 223, C. Columella. CYCLAS. Brug. _Fam._ Conques Fluviatiles, Lam. Conchacea, Bl.--_Descr._ Orbicular, thin, subovate, ventricose, sub-equilateral, equivalve; cardinal teeth minute, one more or less complicated in the left valve, two diverging in the right; lateral teeth elongated, compressed, laminar, acute, doubled in the left valve; ligament external; epidermis thin, horny.--_Obs._ The Cyclades are viviparous, and abound in ditches, ponds, slow streams, &c. in Europe and North America. The genus Pisidium has been separated on account of a difference in the animal, and may be known from Cyclas by being less equilateral, and the anterior side being the longest. Fig. 111, C. Rivicola. CYCLOBRANCHIATA. Bl. The third order of the second section of Paracephalophora Monoica, Bl. containing no genera of Testaceous Mollusca. CYCLOCANTHA. Sw. A genus of "Trochidæ," consisting of Turbo stellaris and T. Calcar, and corresponding with the genus Calcar, Montf.