4 LITTORINIDJi:. 



R. pulcherrima is its solitary representative. In every 

 species ofRissoa the tentacles are pilose ; and R.pulcher- 

 rima lias an unusually long and pointed caudal filament. 



My examination of the Rissoce has been on the same 

 extensive scale as that of the Pisidia. The apology 

 frequently oifered for neglecting such tiny objects is 

 unsatisfactory and unworthy of a naturalist — as if the 

 Creator had bestowed more care in framing leviathan 

 than in constructing the microscopic diatom, or as if 

 the faculty w^hich we enjoy of observing His varied works 

 ought to be restricted to the contemplation of great 

 things as being alone worthy of our exalted notions ! 



Fleming gave the name of Cingula to this genus_, ap- 

 parently being unacquainted with the scientific literature 

 of the continent; and he proposed another genus {Cy- 

 clostrema) for R. Zetlandica. According to Philippi 

 other species were separated by the Baron Bivona, under 

 the generic title of Loxostoma. But such modest at- 

 tempts at classification were far excelled by Leach_, who 

 repudiated Rissoa, and divided it into no less than eight 

 genera_, some of which contained the very same species 

 as those described in others of these so-called genera. 



The species being numerous, it may be convenient to 

 divide them on a conchological basis : — 



A. Cancellated ; outer lip usually strengthened by a rib, and 



sometimes notched within. 1. striatida ; 2. lactea ; 3. can- 

 cellata; 4. calathus ; d. reticulata-, 6. cimico'ides; 7. Jef- 

 freysi ; 8. ijunctura ; 9. ahyssicola. 



B. Eibbed lengthwise and spirally striated ; outer hp thickened 



and reflected. 10. Zetlandica \ 11. costata. 



C. Mostly ribbed lengthwise, and spirally striated ; outer lip 



usually strengthened by a rib. 12. jparva ; 13. incon- 

 spicua; 14. albella ; 15. membranacea ; IQ.violacea; 17. 

 costulata ; 18. striata. 



D. Spirally striated, or smooth ; outer lip plain. 19. proxima ; 



