108 SYSTEMATIC ARRANGEMENT 



centre ; outer lateral elongate, with similar reflexed end ; the end of 

 the inner of the two denticulated. Most like Viviparus (fig. 56). 



Fig. 56.— Teeth of Cerithidia. 



The Cerithideee are found generally in brackish water in man- 

 groves, swamps, and the mouths of rivers. Sometimes they crawl 

 on the leaves and stones in the neighbourhood, and sometimes they 

 are found suspended by glutinous threads to boughs and the roots of 

 the mangroves. Foot broad, suborbicular, expanded. Trunk elon- 

 gate, subcylindrical, annulated. Tentacles short, with the eyes at 

 the tips. 



RissotB are found similarly suspended. — See Gray, Proe. Zool. 

 Soc. 



**** Triphorina. Operculum circular, many-whorled. Shell tur- 

 rited, sinistral. Mouth roundish, with a posterior tubular 

 canal; anterior canal tubular. Tentacles united by a crested 

 veil. 



10. Triphoris. 



Shell turrited. Operculum circular. 

 1. T. perversus, t. 53. f. 2 ; Adams, Gen. Moll. t. 30. f. 4. 



Animal of Triphoris adversus slender. Head broad, short. Ten- 

 tacula long, cylindrical, slender; apex subclavate, far apart at the 

 base, connate by a sinuous veil. Eyes on very short tubercles at 

 the base of the tentacula. Proboscis recondent ? Chin distinct, 

 rather free in front, vibrating. Operculigerous lobe simple. Siphon 

 short. Operculum few-whorled, with a nearly central nucleus. — 

 Loven, Ina. Moll. Scand. 2 1 . 



Triphoris perversus does not form varices in the shell. — Philippi, 

 195. 



The number of granular striae increase with age in Triphoris per- 

 versus of the Mediterranean. The young has only two series of 

 granules ; when more advanced in age, a third, intermediate in posi- 

 tion and smaller, is added ; and in the full-grown shell the last whorl 

 has four distinct series. — Hinds, Ann. fy Mag. N. H. xi. 17, 1842. 



