380 LITTORINID A. 
2? R. apversa, nobis. 
Cerithium adversum, Brit. Moll. iii. p. 195, pl. 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. Grayana, Brit. Moll. iii. p. 70, pl. 71. f. 3,4; (animal) pl. H.H. f. 6. 
We believe that this genus and species will merge into 
Truncatella. See the remarks on 7. 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 Littorine. It inhabits m 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, Risso. 
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 
