BIVALVIA. 69 



Spec. Char. M. tesld clongato-ovatd, obliqud, incurvd, striata; sfriis numerosis, radi- 

 antibus, divaricatis, spatio mediano lavigato ; pedi-regione brevi, marginc rofundato, crenu- 

 laio ; regione dorsali suharcuato. 



Shell elongately ovate, oblique, incurved, striated ; stria) numerous, radiating, and 

 divaricating; middle portion smooth; pedal region short, with rounded and crenulatcd 

 margin; hinge-line somewhat arched. 



Length, 2 inches. 



Localities. Brockenhurst {Edwards). 

 Belgium, lloesselt {Ngst). 



This does not appear to be rare in England. 



I agree in opinion with M. Nyst, that this is quite distinct from M. hastata, Desh., 

 but that it is the one so called by Goldfuss. Our shell agrees precisely with the Belgian 

 fossil. This appears to be intermediate in form between M. elegans and M. hastata ; 

 it has a greater curvature in the ventral region than that of the former, but less so than 

 in the latter, and it attains to a greater magnitude than either. The rays multiply upon 

 the older portion of the shell, having there double the number that there are upon the 

 younger shell. The ventral region is free from rays, and the hinge appears to possess two 

 0!' three teeth. These are wholly irrespective of the denticulated margin produced by the 

 few coarse rays which cover the pedal region. 



12. Modiola Prestwichii, Morris. Tab. XIII, fig. 7. 



Modiola Prestwichii. Morris. Mem. Geo!. Surv., pp. 46, 147, t. 2, fig. 5, 1856. 



— Nystiana. Forbes. Ut supra (name only). 



— — Morris. Catal. Brit. Foss., p. 211, 1854. 



Spec. Char. " M. testa ovato-ehngatd, angustd, subdepressd, sup erne dilatatd, longilu- 

 dincditer striata ,- sfriis numerosis obscuris, marginc crenulato ?" 



" An ovate, elongate shell, of somewhat spathulate form, marked with numerous 

 radiating but rather obscure stria?.'' {Morris.) 



Length, 1 inch. 



Locality. Hempstead Cliff {Morris). 



The name of Nystiana was originally given to this species by the late Prof. E. Forbes, as 

 written upon the plate above referred to. There was, however, no description appended, 

 and the specific name having been already used in this genus, the describer considered 

 himself justified in revoking the one first imposed, and I have for the same reason fol- 

 lowed his example. 



A mass of clay in Mr. Edwards's cabinet, with a surface an inch and a half square, has 

 not less than twelve specimens of various sizes upon it, with the exterior upwards, and it 

 is somewhat singular they should all lie in that position ; they appear to be single valves. 



