^14 SHELLS AND SHELL-FISH. PARTI. 



them together. Their exterior is the most beautiful of 

 all the Trochidce, not merely by the richness and end- 

 less variety of their colours, but from their exterior 

 being almost as highly polished as the olives. The 

 mouth has two cleft and crenated lips ; the tentacula are 

 long, slender, and of equal thickness throughout, while 

 on each side of the body are three lengthened filaments. 

 The PhasianellcB are nearly all natives of the Pacific 

 Ocean, and have an oval-shaped operculum. One 

 species, of a small size, is found in Britain. This is 

 obviously the long-spired group of the Trochidce, re- 

 presenting in this family the Turhidce, the Buccinidce 

 (wherein is Terehra), and the CerithincE. 



(201.) The Senectin^, or snake-shells, were sepa- 

 rated by Humphrey from the Linnsean genus Turbo 

 near forty years ago ; but conchologists have continued, 

 up to this day, to confound the two, or, rather, to mis- 

 apply their names. This most natural group contains 

 nearly all the largest and the most splendid shells of 

 the family, — all of which we believe, possess a circular 

 and very strong stony operculum.* The body- whorl 

 is always ventricose, and is not depressed, like that of 

 the Trochince ; it is produced at its base, in the typical 

 examples, into an obtuse lobe, analogous to the prolong- 

 ation of the base of the zoophagous gastropods, yet 

 without any channel. Thus we perceive, at every step, 

 how completely Nature preserves her uniform principles 

 of representation ; for it is clear that these SenectiiKB 

 represent the zoophagous or channeled tribe, just as 

 Trochus represents the Phytophaga. The snake-shells 

 form themselves into very natural genera. The firsi, to 

 which we retain the sub-family name of Senectus, is 

 known by the spire, although small and short, being 

 always ventricose and pointed, the body-whorl very 

 large, the base produced into a lobe, and the umbilicus 

 altogether wanting. The most gigantic, elegant, and 

 magnificent shells of the whole family enter into this 

 group, which are chiefly natives of the southern hemi- 



* Excepting, perhaps, that type which correfponds to Onustus Humph. 



