130 



The following is a list of the genera, to which all the species of Turbi- 

 nacea at present known may be referred : — 



turritella. 

 Phasianella. 

 Elenchus. 

 Bankivia. 



LlTTOItlNA. 



Margarita. 

 Turbo. 



Trochus. 

 Trochiscus. 

 monodonta. 

 morultjs. 



EOTELLA. 

 PllORUS. 



Solarium. 



Delphinula. 



scalaria. 



monoptigma. 



EULIMA. 



Bonellia. 



lllSSOA. 



Genus 1. TURRITELLA, Lamarck. 



Animal ; disk short, oval, surmounted by a stout pedicle which 

 serves as a support for the head and enters the shell ; head 

 prolonged into a cylindrical rather flattened trunk, broad at the 

 base and cleft at its anterior extremity ; tentacles elongated, 

 with the eyes at the outer base ; mantle forming a fringed ring 

 or collar, variously ornamented according to the species, through 

 which the head passes in and out of the shell. Operculum 

 horny, multispiral. 



Shell; very long, narrow, lurreted ; ivhorls numerous, generally 

 transversely, never longitudinally, ribbed, devoid of spines or 

 tubercles, convoluted into a spiral screiv ; aperture small, some- 

 what round, loith the margins disjoined, lip sharp, never re- 

 flected, broadly sinuated toivards the upper part. 



In speaking of the genus Terehra (ante p. 55), I observed that " the 

 shell of Turritella has very much the form of Terehra, but the aperture is 

 round and entire ; so that Terehra may be likened to a very long drawn-out 

 Buccimm, and Turritella to a similarly elongated Turbo." The comparison 

 cannot, however, be continued with the same force, for the shell of Turbo is 

 of a solid pearly composition, whilst that of Turritella is not, and the animals 

 are somewhat dissimilar,, though the shell of both is alike distinguished by 

 its rounded aperture and by the absence of any basal canal or sinus. It 

 is, indeed, a matter of doubt whether so much importance can be attached, 

 as hitherto, to the canaliculated structure of shells. According to the 

 observations of M. Deshayes and MM. Quoy and Gaimard, there must be 

 a closer relationship than has been yet 'acknowledged between the Turri- 

 tella and the Cerithia and Melanice, although the shell of one genus is 



