84 EOCENE MOLLUSCA. 



7. Arca globulosa (?), Deshayes. Tab. XV, fig. 9, a, b. 



Arca globulosa. Desh. Coq. Foss. de3 Env. de Par.,t. i, p. 209, pi. 33, figs. 4 — 6, 1824. 



Spec. Char. "A. testa ovato-oblongd, brevi, gibbosd, globulosa, suhcordatd, inaqui/aterali, 

 obliquatd, striata, striis alternis minoribus, lavigatis ; car dine arcuato, multidetitato (?) ; 

 margine crenato." — Deshayes. 



Shell ovately oblong, short, tumid, or somewhat globular or gibbous, inequilateral, 

 oVJique, and striated ; strise alternately large and small ; dental margin slightly curved ; 

 ventral margin deeply crenulated. 



Length, |th of an inch ; height, ^th of an inch. 



Locality. Highcliff, Barton. 



This is not particularly rare. I have referred it, with considerable doubt, to the Paris 

 Basin shell. It may possibly be a variety, subglobulosa. 



On comparison with French specimens, I find that the English shell is rather smaller, 

 less quadrate, or more rounded on the siphoni-lateral margin ; and the dental area in the 

 French shell is longer, and furnished with more numerous teeth, 17, 18 {Desh.) ; our 

 specimens have four denticles on one side of the umbo and five on the other ; those on the 

 siphonal side are much inclined, almost parallel with the margin at the extremity, and, 

 from the comparatively great depth of the valve, I imagine that our shell is a full-grown 

 species, and not the fry of a larger one. The sculpture on the exterior resembles that 

 upon A. scapulina, the rays being alternately one large and one small ; the smaller rays 

 are nodulous, and the interspaces are decussated, the lines of growth being large, promi- 

 nent and regular, thickening periodically the smaller rays; but the larger rays are nearly 

 smooth. There appears to be in this species a small triangular fossette beneath the umbo, 

 like that in A. laevigata, dividing the connector into two different arrangements, as in 

 Limopsis. 



8. Arca impolita, J. Sowerby. Tab. XV, fig. 4, a, b. 



Arca impolita. /. Sow. Geol. Trans., 2nd ser., vol. v, p. 136, pi. 8, fig. 10, 1834. 

 — — Morris. Catal. Brit. Foss., p. 185, 1854. 



Spec. Char. A. testa oblongd, conveccd, tumidd, laevigata, glabra ; valde incequilaterali, 

 pedi-regione brevi, rotundatd ; siphoni-regione sub-quadratd ; marginibus intiis integris ; 

 dorsali et ventrali sub-parallelis. 



" Transversely oblong, very convex ; marked with longitudinal rows of punctures ; 

 anterior portion small, rounded ; posterior rounded; front parallel to the hinge-line; shell 

 thin." — /. Sowerby. 



