﻿332 



EOCENE MOLLUSCA. 



Fam . — CYCLOPHORIDiE. 

 Genus 2Sth. — Cyclostoma. Lamarck, 1799. 



Generic character. " Shell turbinated, thin ; axis perforated, aperture oval, peristome 

 continuous, simple or expanded, epidermis thin, operculum shelly paucispiral." 



A large group of land shells have been described under the above generic name, 

 which seem to have only one character in common, viz. a circular mouth, with a thickened, 

 expanded, or reflected peritreme, the shells themselves being some of them nearly 

 cylindrical like C.Jlanulum, or discoidal like C. planorbulum ; and they have in conse- 

 quence been separated into numerous proposed genera, depending for those divisions 

 principally, if not entirely, upon the differences in the angle of volution. 



Two species from our Eocene deposit at Sconce have been described by Mr. Edwards 

 under one of these divisions, called Cyclotm, with a depressedly conical form (see his 

 remarks on the Genus, p. 116 of his work). 



No. 254. Cyclostoma ? mumia, Lamarck. Tab. XXXIV, fig. 2 a — d. 



Cyclostoma mumia, Lamk. An. du Mus., t. viii, pi. xxxvii, fig. 1 a, b, 1806. 



— — Desh. Coq. foss. des Env. de Par., p. 76, pi. vii, figs. 1, 2, 1824. 



— — Id. An. sans Vert, du Bas. de Par., torn, ii, p. 882, 1858. 

 _ _ Forbes. Mem. Geol. Surv. Isle of Wight, p. 68, 1856. 



— — Morris. Catal. Brit. Foss., 2nd edit., p. 244, 1854. 



— — J. W. Lowry. Chart Brit. Tert. Foss., pi. ii, 1866. 

 Megalohastoma mumia. Sandberger. Land- und Siissw. -Conch., p. 217, t. ii, fig. 



20, and t. xv, fig. 16 a— c, 1872. 



Spec. Char. C. " Testa cylindraceo-conicd, transversim striata, striis lojigitudinalibus 

 subtillissimis ; aperturd oblique ovatd ; labro crasso." — Desh. 



Length, 1 inch ; breadth, f ths of an inch. 



Locality. Brading Harbour, Forbes. Sconce, Edwards. 



France, Grignon and numerous other Upper Eocene localities. 



This fossil is said to be abundant in some of the numerous localities given for it in 

 the Upper Eocene beds of France. It is at Grignon in association with many marine 

 shells, and it appears to be there of larger dimensions than our own specimens. It has 

 long been known, and its habits have been frequently a subject of discussion from its 

 occurrence with a marine fauna. In this country specimens are not abundant, and all 

 that I have seen are casts. M. Deshayes describes five distinct varieties : 



