LITTORINA. 25 



LITTORINA, Ferussac. 



Shell turbinate, solid, snbcoiiic or subglobose, with a 

 short spire ; surface smooth or spirally grooved, protected 

 by a more or less developed epidermis ; mouth subeircular, 

 peritreme entire, outer lip sharp-edged, columellar lip 

 expanded, imperforate. Operculum pyriform, corneous, of 

 few rapidly increasing whorls, the spiral nucleus laterally 

 placed. 



Animal having a muzzle-shaped head, with two tenta- 

 cula, bearing the eyes on bulgings at or near their external 

 bases. No neck lobes ; operculigerous lobe without fila- 

 mentary processes. Foot rounded at both extremities, 

 grooved below for the two posterior thirds of its length. 

 Branchial plume single. JNIale organ rather long, linear, 

 bent, crenated on one side, reflected into the branchial 

 cavity. Lateral elements of the tongue subequal, and all 

 with lobed and denticulated apices. 



This excellent genus, which of all its family, approaches 

 most nearly Paludina^ an affinity borne out even by the 

 minute character of its dentition, consists of an assemblage 

 of Mollusks which formerly made part of the hetero- 

 geneous genus Turbo. They all live strictly between 

 tide-marks, and many of them can exist without incon- 

 venience in localities where the sea does little more than 

 occasionally sprinkle them with its spray. 



The Littorina^ or Periwinkles, to call them by their 

 popular name, are distributed through the seas of all 

 climates. Fossil species are enumerated likewise from 

 all formations, even the most ancient, but in this as- 

 signment of the range of the genus there appears to be 

 much error, for assuredly the greater part of the fossils 



VOL. III. E 



