126 CREPIDULA. 



It is divided into the families Tubicolse, Pholadidse, Solenidse, 

 and Myaria. Fig. 44 to 76> 



CRASSISPIRA. Sw. A genus separated from Columbella, 

 Auct. for which Mr. Swainson quotes " Pleurotoma Bottse, 

 Auct." Crassispira fasciata, Sw. Lardn. Cyclop. Malac. p. 313. 



CRENATED. (Crena, a notch.) Applied to small notches, not 

 sufficiently raised or defined, to be compared to teeth. Esc. The 

 hinge of Iridina, fig. 150. 



CRENATULA. Lam. Fain. Malleacea, Lam. Margaritacea, Bl. 

 — Descr. Compressed, foliated, irregular, sub-equivalve, inequi- 

 lateral, oblique; umbones terminal; hinge linear, nearly straight, 

 with a series of excavations, containing the cartilage, while the 

 intervening ridges are covered with the ligament, properly so 

 called. Muscular impression oblong, indistinct. — Obs. This 

 genus is known from Perna by the hinge, which in the latter is 

 composed of a series of regular, straight, ligamentary grooves 

 placed across it. In Crenatula also there is no passage for the 

 byssus, as in Perna. C. Mytiloides, fig. 168. Coasts of the Red 

 Sea. 



CRENULATED. Finely crenated or notched. 



CREPIDULA. Lam. (Crepidula, a little slipper.) Fam. Calyp- 

 tracea, Lam. and Bl. — Descr. Oval, irregular, patelhform; apex 

 lateral, incurved, or sub-spiral; external surface convex, smooth, 

 ribbed, waved, or covered with spines; interior concave, smooth, 

 with a flattish septum reaching nearly half across the cavity ; 

 epidermis light brown. — Obs. The difference between this genus 

 and Calyptreea is that in the latter, the septum is more free from 

 the sides of the shell, so that, instead of forming a regular plate, 

 covering half the aperture, it assumes a variety of shapes, and 

 in some is cup-shaped, in others forked, and in some forms a 

 little angular shelf. Indeed, the variations are so numerous that 

 I think it would be better to throw the two genera into one, and 

 then divide them into smaller groups. Some species of Calyp- 

 treea are farther removed from each other with respect to the 

 characters of the septum and general form of the shell, than 



