72 LITTORINID.E. 



RISSOA. FRiMINVII.LE. 



Shell conical, solid or thin, with a jn-oduced spire ; sur- 

 face smooth or ribbed, spirally or longitudinally striated 

 and grooved, In some species cancellated ; colour various ; 

 mouth ovate, peritreme entire, continuous, outer lip sharp- 

 edged or strengthened by a rib. Operculum ovate, cor- 

 neous, of a few rapidly increasing whorls. 



Animal having a produced muz/.le-shaped head, M'ith 

 two long setaceous tentacula bearing eyes or bulgings near 

 their external bases. No neck-lobes ; operculigerous 

 lobes with developed lateral expansions, and in numerous 

 species with a caudal filament. Foot usually sub-angu- 

 lated in front, acute behind ; in some species rounded at 

 both ends. Lateral elements of the tongue dissimilar, all 

 with denticulated apices ; medium denticle, and its flank- 

 ing laterals very broad, and with lobed incurved apices. 



Almost all the shells which compose this extensive 

 genus are of very small size. They inhabit all depths of 

 water between high-tide-mark, and one hundred fathoms, 

 but the majority of them are dwellers in the laminarian 

 zone. Many are remarkable for beauty of sculpture, others 

 for brilliancy of colour. They are found in all parts of 

 the world, but abound most in the southern parts of the 

 north temperate zone. Several attempts have been made 

 to divide the Rissotz under different genera, but, after a 

 careful considei-ation of their shells, and of the animals as 

 far as known, and not without hesitation we have felt 

 obliged to keep them together, and even to include those 

 curious brackish water forms which have been styled, 

 among other names, Paludinell/E. Should, however, the 

 latter be found to have the posterior part of the foot 



