378 MOLLUSCA. 



Terebka, Brug. 



The. aperture, emargination and columella of a true Buccinum; 

 but the general form is turriculated, that is to say, the spire is length- 

 ened into a point(l). In the 



Cehithium, Brug.j 



Very properly separated from the Murex of Linnaeus, we observe a 

 shell with a turriculated spire; the aperture is oval, and the canal 

 short, but well marked, and reflected to the left or backwards. The 

 animal has a veil on its head, and is furnished with two separated 

 tentacula, on the side of which are the eyes, and with a round, horny 

 operculum. 



Many are found fossil(2). M. Brongniart separates from the Ce- 

 rithia the 



PoTAMiDA, Brongn. 



Which, v/ith the same form of shell, has a very short and scarcely 

 emarginated canal, no sulcus on the upper part of the right margin, 

 and the external lip dilated. The Potamidae inhabit rivers, or at 

 least their mouths, and fossil specimens are found in strata, which 

 contain other fresh-water or land species only(3). The genus 



(1) The whole of the last subdivision of the IJuccina, Gmelin, such as, Bucci- 

 num macvlatum, L., 846, 74; — Hucc. crenulatum,'L. List., 846, 75; — Bucc. dimidi- 

 atum, L., List., 843, 71; — Bucc. subulatum, L., List., 842, 70, &c. 



M. de Blainville separates from tlwm the genus Scbula, which he founds on a 

 difference in the animal, and. moreover on the presence of an operculum. 



(2j Murex vertagus, List, 1020,83; — M. a/wco, List., 1025, 87; — M. annularis. 

 Martini, IV, clvii, 1486;— M. cingulatus, lb., 1492;— ilf- terehella. Id., civ, 1458, 

 9; — M.fuscaius, Gualt., 56, H; — M. graniilaius. Martini, IV, clvii, 1483; — M. mo- 

 luccanus, lb., 1484, S. Sec, with the numerous fossil species described by M. de 

 Lamarck, Ann. du Mus. M. Deshaycs has separated from the Cerithia, under the 

 name of Nevinea, some small species, where the margin is prolonged into the 

 aperture, and divides it into three distinct orifices. 



It is also near the Cerithia that we must place several fossil shells, which form 

 the genus Nerinea of M. Defrance, and which is distinguished by strongly marked 

 plicse on each whorl and on the columella, the centre of which, besides, is hollow 

 throughout. Nine species are already ascertained. 



(3) See Brongn., Ann. du Mus., XV, 367. In this subgenus should be placed 

 the Cerithium atrum, Brug., List., pi. 115, f. 10; — Cer. palustre, f. lb., 836, f. 

 62; — C. muricaiian, lb., 121, f. 17, &c., and among the fossils, the Potamida La- 

 markii, Brongn., loc. cit. pi. xxli, f. 3. 



