RISSOA. 76 



always rounded, and the operculigerous lobe constantly 

 destitute of a caudal filament ; and, on the other hand, 

 the truly marine species to have the caudal termination 

 constantly acute, and the operculigerous lobe always pro- 

 vided with a cirrhus, then we may have sufficient grounds 

 for separating the two groups. At present, however, we 

 cannot assert such differences in the animals to be con- 

 stant, and, as to the shells, a generic distinction founded on 

 them will not in this instance hold good, since assuredly 

 the latter characters of the animal in known instances 

 accompany forms of shells, which, though truly marine, 

 cannot be definitely distinguished from the Paludinella'. 



The Bissoa undoubtedly existed during the oolitic period; 

 brackish water species of the genus are abundant in the 

 Purbeck rocks ; so similar, too, are they to existing 

 forms, that it requires a very critical eye to mark their 

 differences. 



R. STRIATULA, MoutagU. 



Short, strong ; whorls encircled by acute prominent carince, 

 whose interstices are traversed by densely-disposed minute lon- 

 gitudinal striae. 



Plate LXXIX. fig. 7, 8. 



Turbo carinatus. Da Costa, Brit. Conch, p. 102, pi. 8, f. 10. 



Turbo striatulus, (not of Linn.) — Mont. Test. Brit. vol. ii. p. 30G, pi. 10, f. 5. — 

 Maton and Rack. Trans. Linn. Soc. vol. viii. p. 172 (not 

 diagnosis). — Rack. Dorset Catalog, p. 50, pi. 14, f. 10. — 

 TuRT. Conch. Diet. p. 212. — Dillw. Recent Shells, vol. ii. 

 p. 857.— Wood, Index Testae, pi. 31, f. 100. 

 „ monilis, Turt. Conch. Diction, p. 200 (fide Jeffreys from type). 



Cingida striatula, Fleming, Brit. Animals, p. 305. — Brit. Marine Conch, p. 175, 

 f. 45. 



Hissoa „ Recluz, Revue Zoolog. Cuvier. 1843, p. 9. 



LUtori7ia „ Brown, Illust. Conch. G. B. p. 17, pi. 10, f. 33, 34. 



Although assuredly not the Turho striatulus of Lin- 

 naeus, which we regard as a lost species, since the types 



VOL. III. L 



