FAMILY CERITHIIDJS. 



Shell spiral, elongated, many whorled, frequently varicose, the- 

 surface usually tuberculated, spinose or costulate ; aperture chan- 

 neled in front, the outer lip generally expanded in the adult. 

 Operculum corneous, spiral with central or sublateral nucleus. 



Animal with a short contractile muzzle, distant, slender tentacles 

 and eyes on peduncles connate with the tentacles or sessile at their 

 base ; mantle margin with a short, rudimentary siphonal fold. 



Dentition. The usual formula is 2'l'l'l-2 (PI. 19, figs. 1, 2) r 

 but in Triforis the marginal teeth are multiplied 4'1'1'1*4 (PI. 19,. 

 fig. 3). 



The Cerithiidse occur principally about tropical and semitropical 

 shores, on rocks or among marine plants, littoral or in shallow 

 w r aters. Many of them are estuary mollusks, and some inhabit 

 fresh waters. 



The shell is very variable in form, and especially in the anterior 

 canal of the aperture, which is always short, but sometimes disap- 

 pears completely. 



The Cerithiidse have been monographed by : 



Kiener. Coquilles vivantes. 81 species. No date. 



Sowerby. Thesaurus Conchyliorum, ii. 184 species. 1855. 



Sowerby. Reeve's Conchologia Iconica, xv. 232 species. 

 1865-6. 



Dr. Jousseaume has recently published a monograph of Triforis,. 

 of which he has made a family, with a number of genera (Bull. 

 Soc. Mai. France, i, 217, 1884). 



Genus CERITHIUM, Adanson, 1757. 



Shell turreted, imperforate, many whorled, tuberculate usually, 

 with indistinct varices ; aperture small, with a short posterior chan- 

 nel and a better marked oblique one in front, outer lip expanded, 

 inner lip thickened, concave. Operculum corneous, paucispiral, 

 with submarginal nucleus. Animal (PI. 19, figs. 14, 13) truncated 

 and grooved in front, attenuated behind ; muzzle large and long, 

 sinuated at the end, tentacles thickened posteriorly and bearing eyes 

 externally at a short distance from their base ; siphon short. Foot 

 secreting a mucous thread by which the animal is able to suspend 

 itself (PL 19, fig. 6). Some of the species emit a bright green fluid 

 when molested. 



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