90 CALLITHEA. 



CALCAREOUS, {calx, lime.) A term applied to a shell or to its oper- 

 culum which is composed principally of lime or shelly matter, as is 

 usually the case, in distinction from one which is of an horny, mem- 

 branaceous texture. The greater number of shells are calcareous, 

 but it forms an important point of distinction with regard to the 

 operculum. The only difference between the genera Trochus and 

 Turbo, as at present established, depends upon the calcareous 

 or shelly, and the corneus or horny texture of the operculum. 



CALCEOLA. Fam. Rudistes, Lam. and Bl. — Bescr. Equilateral, 

 inequivalve, triangular ; umbones separated by a large triangular 

 disc in the lower valve ; cardinal margin straight, linear, dentated ; 

 lower valve large, deep; upper valve flat, semi- orbicular, forming 

 a kind of operculum to the lower. — Obs. This singular shell, 

 known only in a fossil state, in the Palaeozoic beds, is placed by 

 Linnaeus in the genus Anomia. Lamarck places it among his 

 Rudistes, but Mr. Sowerby in his genera of Shells, states that it 

 should be added to the family of Brachiopoda, Fig. 194, 195. 

 C. Sandalina. 



CALLANTICA. Gray. Pollicipes hispidus, Leach. 



CALLIA. Gray? A genus described as having a peculiarly polished 

 shell like Pupina, but wanting the notch. 



CALLISOSTOMA. Sw. A genus of shells separated from Trochus, 

 and thus described, " Imperforate ; spire elevated, acute ; aper- 

 ture broader than high, transversely ovate, hardly sinuated at the 

 base, and slightly oblique ; shells always smooth, and often po- 

 lished." C. zizyphina is mentioned as an example. 



CALLIRHOE. Montf. p. 362, vol. 2. Appears to be figured from 

 the nut or inner portion of a large Belemnite. 



CALL1SCAPHA. Gray? Iridina Nilotica, Sow. Zool. Journ. 1. 

 pi. 2. Separated from Iridina on account of the hinge margin 

 being smooth. 



CALLITHEA. Sw. A sub-genus of Mitrae, consisting of those 

 species, which like M. sanguisuga, have the " spire and aperture 

 of nearly equal length ; internal channel nearly obsolete ; shell 

 with longitudinal linear ribs, crossed by transverse striae and 

 bands ; base contracted." Swainsoii Mallac. Lard. Cyclop. 



