Cerithium. MOLLUSCA. CERITHIAM1. 357 



Trans, vii. 117. t. xi. f. 2.— Murex def. Sower. Min. Conch, t. ccccxi. f. 1 — 

 In London Clay. 



8. T. sexdentatus. — Ovate acuminated, costated, longitudinally striated, 

 transversely carinated ; whorls convex ; aperture elongated, with five or six 



teeth within its outer lip Murex sex. Sower. Min. Conch, t. ccccxi. f. 3. — 



Marine formation, Colwell Bay, Isle of Wight. 



CERITHIADiE. 



a. Marine. 



Cerithium. 

 (Strutheolaria.) 



aa. Fluviatile. 

 Potamedum. 

 Melanopsis. 

 (Pirena.) 



Gen. LXXXII. CERITHIUM.— Outer margin of the aper- 

 ture rounded, with an obsolete canal, in many species, at its 

 retral junction with the body-whorl. 



— 352. C. costatum.' — Whorls ten, a spiral line at the base of 

 each, becoming double on the body-whorl. 



(Stromhiformis costatus, Da Costa, Brit. Conch. 118. t. viii. f. 14.) Strom- 

 bus cost. Don. Brit. Shells, t. xciv. Mont. Brit. Shells, 255 — English 

 coast, rare. 

 Length about half an inch ; brown ; tapering to a fine point ; transverse 

 ribs numerous, rounded, slightly waved; aperture ovate; the outer lip a lit- 

 tle expanded ; inner lip smooth ; canal very short and patulous. 



353. C. turbiforme. — Whorls seven, destitute of a thread-like 



spiral line at the base of each. 



Mont. Test. Brit. Sup. 110. t. xxx. f. 7 — Found by Mr Laskey on the 

 shores of Nun's Island, Iona. 



Length about a quarter of an inch ; breadth two-thirds less ; brown ; aper- 

 ture white ; whoi'ls well-defined by the separating line ; transverse ribs about 

 eighteen ; base smooth ; aperture suborbicular ; outer lip thickened at the 

 margin, and a little spreading. 



EXTINCT SPECIES. 



1. C. pyramidalis. — Pyramidal, with six projecting tuberculated angles; 

 whorls ten or eleven, transversely tricarinated, carina? tuberculated ; six com- 

 pressed tubercles on the upper part of the last whorl ; outer lip expanded. — 



(Murex angulatus, Brander, f. 46.) Sower. Min. Conch, t. cxxvii. f. 1 



London Clay. 



2. C. geminatum. — Conical, elongated, smooth, with seven or eight longitu- 

 dinally disposed pairs of acute tubercles on each whorl ; whorls about twelve, 

 lip even. Sower. Min. Conch, t. cxxvii. f. 2. — London Clay. 



