358 On a new Arrangement of British Rissose. 



XXXVI. — On a nciv Arrangement of British Rissose. 

 By H. and A. Adams. 



To the Editors of the Annals of Natural History. 



Gentlemen, Haslar Hospital, Gosport, Oct. 6, 1852. 



In revising the Rissoce for the " Genera of Recent Mollusca " 

 about to be published, we found the group composed of most 

 dissimilar forms. The recent observations of the learned and 

 accurate William Clark have enabled us to offer a new distribu- 

 tion, an outline of which, perhaps, you may think worthy of a 

 place in your ' Annals.' 



We are. Gentlemen, your most obedient servants, 



H. and A. Adams. 



Genus Rissoa, Fremenv. (Acme, Hartm.) 



Opercular lobe with a single distinct cirrhus. Shell with the 

 outer lip dilated ; spire elevated. 



R. labiosa. R. costata. R. parva. 



Genus Alvania, Risso. (Cyclostrema, Flem. Turbona, Leach.) 



Opercular lobe winged ; three caudal cirrlii. Shell turbinate, 

 cancellated ; outer lip varied. 



A. cimex. A. reticulata, 



A. calathiscus. A. abyssicola. 



A. striatula. A. zetlandica. 

 A. lactea. 



Genus Cingula, Fleming. (Sabinea, Leach.) 



Opercular lobe and caudal cirrhus indistinct and rudimentary. 

 Shell banded; spire elevated; outer lip simple. 

 C. cingillus. 



Genus Onoba, nobis. (Turbonilla, Leach, non Risso.) 



Opercular lobe winged, no caudal cirrhus. Shell spirally 

 striated ; outer lip simple. 

 O. striata. 



Genus Paludinella, PfeifFer. 



Tentacles short, obtuse; eyes sessile on their \ipper surface 

 near the middle. Opercular lobe and caudal filaments none. 

 Shell orbicular, thin, umbilicated, covered with an epidermis. 

 P. littorea, Chiaje. 



