118 MOLLUSCA FROM THE CRAG. 



Fig. 7 b is a young or perhaps broken specimen ; the straight part of the tube 

 in fig. 7 a is nearly cylindrical. 



If Serpida incrassata of Walker be the young of Cacum glabrum^ it is probable 

 the shell from the Crag may be the young state of Cacum mammittatum. 



Littokina,* Ferussac, 1821. 

 Turbo (spec). Linn. 

 Tricolia (spec.) Eisso. 

 Neritoides. Brown, 1827. 

 Litorina. Loven, 1846. 

 Melarapha. Megerle, 1832 (fide Gray). 

 Gen. Char. Shell turbinate, thick, solid, and strong, ovate or globular ; spire 

 acuminated, consisting of few volutions ; externally smooth or striated ; aperture 

 elliptical or subcircular ; peritreme entire, sharp-edged ; columella rather flattened ; 

 operculum corneous and spiral, with lateral nucleus. 



Shells of this genus have a strong resemblance in form to those of Turbo, with 

 which they have been generally placed. A considerable difference exists in the 

 animal inhabitants, and in the recent state they may be distinguished by the oper- 

 culum, which in this genus is thin and corneous, while in Turbo it is calcareous, 

 thick, and ponderous ; in which genus, also, the shells are of a nacreous texture. 

 They may be distinguished from Phasianella, which they somewhat resemble, by the 

 want of a polished and glossy exterior. 



These animals, as the name implies, are frequenters of shallow water, near the 

 shore, and are generally found in salt water. 



As a genus, it has an extensive geographical range, being found in all latitudes ; 

 and a species is given by Mr. J. Sowerby as belonging to the Silurian system. 



1. Littoeina littoeea. Linn. Tab. X, fig. 14, a — Jc. 



Turbo littoreus. Linn. Syst. Nat. 12th edit. p. 1232, 1766. 



— Brown. Illust. Brit. Conch, pi. 46, fig. 1-9, 1827. 



— — J. Sow. Min. Conch, t. 71, fig. 1, 1814. 



RUDIS. - - - t. 71, fig. 2. 



— littoreus. Smith. Strata Identif. p. 5, pi. 2, fig. 3, 1816. 



— carinatus. Woodward. Geol. of Norf. t. 3, fig. 11, 1833. 



— VENTRICOSUS. .... fig. 12. 



BICARINATUS. ..-. fig. 13. 



SULCATUS. - - - - fig. 14-15. 



— ELONGATUS. - - . - - fig. 16-18. 

 Delphinula CARINATA. --- - fig. 9. 

 Littorina vulgaris. G. Sowerby. Gen. of Shells, fig. 1. 



— squalida. Brod. and Sow. Zool. Journ. vol. iv, p. 370, 1829. 



— — Gray. Zool. of Beechey's Voy. pi. 24, fig. 12. 



— littorea. 5. Wood. Catalogue 1842. 



— — Nyst. Coq. foss. de Belg. p. 387, 1844. 



L. Testa variabilis ovafd, imperforatd, lineis fuscis cinctd ; apice acuto ; anfractibus 



* Etym. Littus-oris, the shore. 



