256 Lamarck's Genera of Shells. 



This section contains five families ; in the two first the canal 

 at the base of the aperture is always manifest ; in the third it 

 disappears, and the two last have only a notch, and a small, 

 low, inclined margin. 



1st Family. 

 Canalifera. (11 Genera.) 

 Shell with a canal, variable in length, at the base of the 

 aperture, the right margin of which does not alter by age. An 

 operculum. 



This family is separated into two divisions. 



1st Division. 

 No constant varix on the right lip. 



1. Cerithium *. 

 Shell turrited. Aperture short, oblong, oblique, terminated at 

 the base, by a short truncated or curved canal ; never notched. 

 A slight channel at the upper extremity of the right lip. Oper- 

 culum small, orbicular, horny. 



The spire of the shell constitutes at least two thirds of its 

 whole length; the last whorl being but little larger than the 

 preceding one, the shell has the form of an elongated pyrami- 

 dal cone ; surface generally striated or tubercular, and some- 

 times varicose. 



A thorough knowledge of this numerous genus is very im- 

 portant to the modern geologist. 



Type. Cerithium palusti'ef. (Strombus palustris. Linn.) 



Shell turrited, thick, longitudinally plicate, transversely stri- 

 ated, brownish ; whorls tri-striated, the last with very numerous 

 sulciform stria ; lip sub-crenate. 



East Indies. PI. VIII. Fig. 173. 36 recent species, and 60 

 fossil. 



2. PleurotomaJ. 

 Shell turrited, or fusiform, terminated at the lower part by a 



" From Cerites, a Rem of a waxen colour '/ 



t Wthe marshes; Lamarrk's 2d genus; his type is C. giganteum. 

 t From •arXEufa, the side, and rifxin to cut, denoting the characteristic fissure 

 on the right lip. 



