MOLLUSCA. 107 



dismembered by modern conchologists, in consequence of 

 Lamark having restricted the character in the following 

 terms : " Testa univalvis, conoidea vel subturrita. Aper- 

 tura integra rotundata, edentula ; marginibus superne sem- 

 per disjunctis; columella basi planulata." Our T. littoreus 

 is now considered as constituting the genus LITTORINA. 



In the genus SCALARIA, the mouth is circular and bor* 

 dered, with the margins united. The spires are covered 

 with raised edged, slightly oblique, longitudinal ribs. The 

 famous wentletrap is the type of the genus. 



Lamark thus defines his genus DELPHINULA : " Testa 

 univalvis subdisco'idea vel abreviato conica, solida, margari- 

 tacea, umbilicata ; anfractibus subasperis. Apertura rotun- 

 data, marginibus orbiculatim connexis." The T. delphinus 

 is the type of the genus. There are many species of tur- 

 bines common on our shores, which are excluded by the 

 preceding characters from the genera turbo and delphi- 

 nula, such as the striatus, cingellus, bryereus and others. 

 They are distinctly turreted, with the margins of the moutli 

 united, and constitute a genus termed CINGULA. 



The Turbo terebra of Linnaeus serves as the type of an- 

 other genus, termed TURRITELLA, in which the margins of 

 the mouth are disjoined, the spire regularly turreted, and 

 the lip emarginated by a sinus. Nearly allied to the pre- 

 ceding is the genus PHASIANELLA, which Lamark thus de- 

 fines : " Testa univalvis, ovata vel conica, solida. Apertura 

 longitudiiialis, ovata, integra ; labro simplici acuto. Colu- 

 mella laevis basi attenuta. Operculum calcareum vel cor- 

 neum animali adherens." 



Perhaps a rigorous examination of the turbines of British 

 writers might justify the formation of one or two new gene- 

 ra. In the genus ODOSTOMIA, the columella is furnished 



