135 



more proboscis-like head, and has no fringed collar or digitated processes. 

 The shell differs from Phasianetta in not possessing the same beautiful 

 porcelain surface, but on the contrary numerous varieties of sculpture, 

 and from Turbo in being of uniformly smaller size, and never pearly. 



The Littorina appear to be very generally distributed in both hemi- 

 spheres, but it will not be possible to notify their localities, or form an 

 estimate of their number, until the species have been collected and named. 

 "They dwell," says M. Deshayes, "as their title indicates, on the rocks 

 along shore, and are almost always out of the water, placing themselves 

 within reach of the spray." 



The miscellaneous assemblage of genera comprehended in the family 

 Littorinidce of Mr. Gray's Synopsis, have but a remote affinity with the 

 group represented by the present genus. 



For List of Species see Appendix. 



Figure. 



Littorina pulchra. PI. 12. Fig. 60. Shell, showing its rounded-ovate 

 aperture and slightly expanded lip. — From Mr. Cuming's collection. 



Genus 6. MARGARITA, Leach. 



Animal ; similar to that of Trochus.* 



Shell ; turbinated, sometimes rather depressed, sometimes large!// 

 umbilicated, outer surface smooth, /polished, with, in many in- 

 stances, a shining horny epidermis, inner surface delicately 

 pearly, iridescent ; margins disjoined, lip simple, acute. Oper- 

 culum horny, spiral. 



The animal of this genus, according to the testimony of M. Deshayes, 

 differs in no respect from that of Trochus, yet the shell presents a singular 

 peculiarity of character, constant alike in all the species. They are, how- 

 ever, susceptible of being divided into two very distinct groups, one of 

 rather light spiral structure, largely umbilicated, of very much the form of 

 Cyclostoma, the other, to winch the species selected for illustration belongs, 



* Fide Deshayes. " Grace a 1' extreme obligeaucc de M. Janclle, nous avons de Spitzberg 

 T animal d' ime espece qui pourrait eutrer dans le genre Margarita, et cet animal ue dillere en 

 rien de eelui de Trochus." — Anim. sans vert, vol ix. p. 185. 



