RissoA. 329 



coronata, Recluz. Isevissima, 0. B. Adams. 



curta, Soiv. princeps, C. B. Adams. 



decussata, Sow. semiglabrata, A. Adams. 

 eulimoides, A. Adams. 



Genus RISSOA, Freminville. 



Opercular lobe with a single, distinct cirrhus at the hind 

 part. 



Operculum ovate, subspiral, simple. 



Shell usually white, solid, conical ; spire pointed, many- 

 whorled, whorls convex, smooth or longitudinally ribbed ; 

 aperture ovate ; outer lip more or less dilated and thick- 

 ened externally. 



Syn. Loxostoma, Bivon. Lamarckia, Leach. Ris- 

 soaria, Agass;. Gonostoma, Muhlf.y not Held. Anatasia, 

 Gist. 



Ex. R. monodonta, Philip pi, pi. 35, fig. 2. Oper- 

 culum, R. labiosa, Montagu, fig. 2, a, 2, h. Shell, R. la- 

 biosa, fig. 2, c. 



In this genus the operculigerous lobe is furnished pos- 

 teriorly with a single cirrhus or tapering filament ; the 

 species are very numerous, and are usually of a white 

 colour ; they are found in all parts of the world, living 

 among sea-weed in shallow water. 



Species of Rissoa. 



aberrans, C. B. Adams. costata, Adams. 



albella, Loven. crassicostata, C. B. Adams. 



arata, Phil. elegans, A. Adams. 



bulimoides, C. B. Adams. elongata, Phil. 



Caspica, Eichw. exarata, Stimp. 



castanea, Recluz. excavata, Phil. 



cornea, Loven. exigua, Midi. 



VOL. I. U U 



