GASTEROPODA. 123 



tances upon the volution, becoming nearer together towards the lower part, and 

 terminating with one that is elevated into a sort of keel, encircling the umbilicus, 

 which is broad and naked, but not very deep. 



Teochus,* Linn. 

 Pyramis. Schum. 1817. 

 Ziziphinus. Leach, 1819. 

 Gibbula. Id. 



Stekomphala. Id. 

 Pyramidea. Swainson, 1840. 

 Calliostoma. Id. 



Gen. Char. Shell conical, with a more or less elevated spire, thick, strong, and 

 of a nacreous texture ; apex generally acute, sometimes depressed and obtuse ; base 

 flatfish, with a carinated edge to the volutions ; aperture square or rhomboidal, 

 with an oblique columella, parallel to the outer lip ; operculum corneous and spiral. 



This is a marine genus, and not restricted to any climate, being found in all 

 parts of the world. It is also of great antiquity ; it appears first in the Protozoic 

 rocks. Mr. G. B. Sowerby, in his genera, has separated Trochus from Turbo by 

 the distinguishing character of a corneous operculum for the former, and a testa- 

 ceous one for the latter ; these two genera merge so imperceptibly into each other 

 that they are not to be defined by the form of the shell alone, although the species 

 of this genus are generally more truly conical. 



Sect. a. IMPERFORATE. 

 1. Teochus ceenulaeis. Lam. Tab. XIII, fig. 7, a — b. 



Trochus crenulakis. Desk. Coq. foss. des Env. de Par. p. 229, pi. 27, fig. 3, and pi. 28, fig. 13, 15. 

 — Bowdich. Elements of Conch, pi. 9, fig. 7, 1822. 



Tr. Testa eloncjato-conicd, pyramidatd, elevatd, imp er for at a ; transversim tuberculoid ; 

 anfractuum margine inferiore crasso, tuber cutis inajoribus crenato ; columella truncatd, 

 incrassatd. 



Shell pyramidal or elongato-conical, imperforate ; sides rather flat, ornamented 

 with transverse tuberculated strise, inferior one most prominent ; base flat ; aper- 

 ture trapeziform, with a truncated columella, thickened, or unidentated at the 

 lower part. 



Axis, 1 inch. 



Locality. Cor. Crag, Gedgrave. 



The specimen from which the figure was taken is the only one I have seen ; it 

 was obligingly sent to me by Mr. Charlesworth for description ; it is from the 

 cabinet of H. Davey, Esq., of Beccles, and was purchased, among other Crag 

 fossils, at Orford, in Suffolk. This specimen so precisely resembles some of my 

 Grignon shells, that it is requisite to record the manner it has come into my pos- 

 session, as there is a slight doubt respecting the locality, and unfortunately there 



* Etym. Trochus, a top. 



