﻿SUPPLEMENT TO THE BIVALVIA. 



1!) 



2. Cyclas tumidula, S. Wood. Tab. B, fig. 4 a, b. 



Cyclas exigua ? S. Wood. Lond. Geol. Journ., p. 118, 1847. 



Spec. Char. C. Testa minima, ventricosd, tenui, ovato-transversd, subcsquilaterali, 

 laevigata, glabra, antice rotundatd, obtusd, postice angustiore et lutiore ; umbonibm 

 minimis, vix prominentibus, parum obliquis. 



Length, of an inch ; height, -y^ths of an inch. 



Locality. Headon Hill (S. Wood). 



The shell which I have here called tumidula appears to be more inflated than any other 

 known to me. It is very smooth and glossy, with a short dorsal margin, the umbo 

 slightly prominent, and the shell is nearly equilateral. It resembles from descriptions 

 and figures two or three other species, viz., 1st Cgclas VerneuiUi de Boissy, ' Mem. de la 

 Soc. Geol. de Prance,' 2nd ser., t. iii, p. 270, pi. 5, fig. 5 ; figured also by M. 

 Deshayes, 'An sans Vert, du Bas. de Par.,' pi. 34, figs. 40 — 42, but that shell does not 

 appear so tumid as ours. 2nd. Spheerium castrense, Moulet, which has been figured 

 and described by Sandberger, ' Land- und Siissw.-Conch.,' p. 221, tab. xiii, fig. 1, but this 

 also appears less tumid and more transverse than my shell. 3rd. Cgclas elegans, Gould, 

 ' Inv. Massach.,' p. 74, fig. 55, a recent species from the north-east coast of America. 

 This latter approaches near to our Headon Hill shell, but is also less tumid. I have not 

 been able to see the interior of my shell, but it seems to differ from C. Bristovii in being 

 more tumid and equilateral. 



In the year 1843 I found in the truly freshwater bed at Hordle a very small 

 specimen of a shell belonging to this genus, to which I gave the name of Cgclas exigua in 

 the ' London Geol. Jour.' Mr. Edwards not having in his cabinet a corresponding 

 specimen, I gave him the one referred to under this name of exigua, but I have not 

 been able to detect it in his collection now in the British Museum so as to determine 

 whether it be the same as that now figured as tumidula, but to prevent confusion I 

 have, under the circumstance of the shell apparently not having been preserved by 

 Mr. Edwards, given it as the same as tumidula. 



