FAMILY CERITHIID^. 



Shell spiral, elongated, many whorle<l. frequently varicose, the 

 surface usually tnberculated, spino.se or costulate ; aperture chan- 

 neled in front, the outer lip <renerally 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 

 ha-e : mantle margin with a short, rudimentary siphonal fold. 



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

 hut in Triforis the marginal teeth are multiplied 4'1*1'1'4 (PL 19 r 



>). 



The (Vrithiidae occur principally about tropical and semitropieal 

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

 water-. Many of them are estuary mollusks, and some inhahit 

 fre-h waters. 



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

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

 pear.- completely. 



The (Vrithiida 1 have been monographed by: 



Kieiier. ('Kjuilles vivantes. 81 species. Xo date. 



Souerby. Thesaurus Conchyliorum, ii. 1*4 species. 1855. 



Sowerby. Reeve's Conchologia Iconica, xv. 232 specie-. 

 186.5-6. 



I>r. Jousseaume has recently published a monograph of Trifori-. 

 of which he has made a family, with a number of genera (JJit/L 

 Soc.M><!. France, /, 217, 1*M . 



Genus CERITHUM, A^danson, 17.~>7. 



Shell turreted. imperfi.rate, many whorled. inbercnlatc usually, 

 with indi>tinct variee- ; aperture small, with a short posterior chan- 

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

 inner lip thickened, concave. Open-ulnm corneous, pauci-piral, 

 with -ulmarL r inal nncleii-. Animal < 1M. l!i, !iirs. 14, l-'l) truncated 

 and irn.oved in front, attenuated behind; mu/./le lar.ire and long, 

 -iimated at the riid. tentacles thickened jn^teriorly and hearin- 



iially at a -h-.rl di-tance fn.m their lia>e ; >i].hoii short. Foot 

 'in.-- a mucoii- thread by which the animal is aide to suspend 

 it-elf ' PL 19, fig. 6). Some of the ipeciaa emit a bright green fluid 

 when molested. 



112 



