380 LITTORINID.E. 



? ? B/. ADVERSA, nobis. 



Cerithium adversum, Brit. Moll. iii. p. 195, pi. 91. f. 5, 6. 

 Murex adversus, Montagu. 



If the animal should be found to have a floating respiratory 

 mantellar canal and a proboscidal head, it will of course 

 belong to Murex ; but I do not believe that any Muricidal 

 species has a laxly spiral operculum. I therefore repeat that 

 the ' adversus } belongs to the Cerithium of authors, which is 

 only another term for an elongated Rissoa that has a spiral 

 operculum, long strong muzzle, armed with a lingual riband, 

 doubled into a pair of jaws at the anterior extremity. 



ASSIMINIA, Gray, Leach. 



A. GRAYANA, nonnull. 

 A. Gray ana, Brit. Moll. iii. p. 70, pi. 71. f. 3, 4; (animal) pi. H.H. f. 6. 



We believe that this genus and species will merge into 

 Truncatella. See the remarks on T. littorea. 



Animal spiral, yellowish-brown ; mantle simple ; head with 

 a moderately long, deeply-cloven annulate muzzle. Eyes at 

 the extremities of pedicles soldered to the shortish blunt 

 tentacula, being of concurrent length with them ; a canali- 

 ferous groove runs from their bases to the branchial cavity. 

 Foot large, broad, auricled, truncate in front, with an obtuse 

 posterior termination, double-lobed ; the upper one, being 

 much the smaller, carries the usual horny, suboval, spiral 

 operculum of the Littorina. It inhabits in sufficient abun- 

 dance the small streams which discharge into the Greenwich 

 marshes, but generally within the reach of the tidal and 

 brackish waters. The animal has not occurred to us. 



TRUNCATELLA, Eisso. 



Exmouth, June 8, 1853. 



Mr. Wm. Thompson, of Weymouth, has this day favoured 

 me with some lively examples of the rare Truncatella Montagui 

 in its adult and young states, that is, before and after the 

 truncature of the apex, and also others of the still rarer Rissoa 



