358 LITTORINID^E. 



white. Operculigerous lobe small ; the alse anteriorly are mere 

 lines, but exposed posteally in flat limited curves, carrying 

 far behind a suborbicular, pale yellowish- white, very indistinct, 

 paucispiral operculum, obliquely finely interstriated, with a 

 sunken nucleus : no caudal cirrhus : the edge of the operculum 

 is marked with a fine brown line. 



The animal is free, but the progression is not direct; it 

 often jerks or screws the shell a quarter of a round, and carries 

 it almost perpendicularly ; it is abundant in the middle littoral 

 levels near Exmouth. 



Though this species differs in many points from the typical 

 Rissoce, still there is nothing so essentially different as to 

 require a new genus ; and I am o*f opinion that the newly 

 constituted genera Paludinella and Hydrobia are unnecessary, 

 and not generically separated from Rissoa. 



R. INCONSPICUA, Alder. 



R. inconspicua, Brit. Moll. iii. p. 113, pi. 76. f. 7, 8, and pi. 82. f. 5-9. 

 R. pulcherrima, Brit. Moll. iii. p. 129, pi. 85. f. 1, 2. 

 Turbo albulus ? Adams, Linn. Trans, iii. pi. 13. f. 17, 18. 



Shell ovately conic, pointed, with 6-7 moderately-raised 

 volutions, very pale yellowish-white, marked with two rows of 

 longitudinal, distantly separated, dull yellow or rufous irre- 

 gular linear blotches on the body, and one on the antepenulti- 

 mate whorl. The sculpture is very variable, sometimes almost 

 smooth, at others with close-set, longitudinal costellse, showing 

 all the phases of strong and fine lines, crossed at right angles 

 by finer ones. There are one or two grooved circular lines at 

 the base of the body volution. The aperture is suborbicular, 

 and the outer lip has the callous pad of the Rissoa. Axis 

 Tifthj diameter -rrth of an inch. 



Animal. Ground colour white, blotched with yellow and 

 dark smoke hues. Mantle entire, except that at the upper 

 angle of the aperture it has the pendant filament so often 

 seen in the Rissoa, and the use of which still remains doubt- 

 ful. Rostrum short, cloven, carrying the buccal disk beneath, 

 with its vertical fissure, and the usual masticatory apparatus 

 of a pair of jaws, corneous palate, and tongue ; it is tinged 



