1852.] MORRIS THANET SANDS FOSSILS. 265 



margin, which is rather straight ; surface minutely granulated, and 

 transversely striated and undulated. This shell is difficult to 

 distinguish from the P. intermedia, Sow., and appears to be inter- 

 mediate in general form and character to that species and the P. cor- 

 rugata, Sow. (Dixon's 'Fossils of Sussex'); the ligamental and ventral 

 margins are straighter, and the shell more compressed ventrally than 

 P. intermedia. The surface is also minutely granulated, which 

 character has not been observed in the other species. 



The difference of habitat may, however, have modified the forms 

 assumed by these shells, producing only local varieties. 



The P. intermedia of Nyst appears to be distinct from the English 

 forms. 



Heme Bay. Mr. Bowerbank's Collection. 



Pholadomya Koninckii, Nyst, Plate XVI. fig. 4. 

 (Nyst, Coq. Foss. Belgiques, p. 50. t. 1. f. 9.) 



It has been considered advisable to refigure this shell, as it has not 

 been previously described as occurring in England ; and especially, 

 as this species has been sometimes mistaken for P. margaritacea. 

 Sow. But, from comparison with authentic specimens, we have 

 considered this to be a variety of P. Koninckii, Nyst, a species very 

 characteristic of the Lower Tertiaries of Belgium. 



Heme Bay. Mr. Prestwich's Collection. 



Cytherea orbicularis, Edwards, MSS. Plate XVI. fig. 5. 



Testa tenui, orbicular!, depressa, lentiformi, subsequilaterali, vix transversa, cou- 

 eentrice striata vel sublamellosa ; iimbonibus minimis, subrecurvis ; lunula vix , 

 notata. 



A slender, orbicular shell, with faintly marked concentric striae or 

 lines of growth, becoming occasionally lamelliform ; the umbones 

 are small and slightly recurved ; the sinus in the pallial impression 

 is obtusely angular ; the lunule is nearly obsolete. 



This species varies slightly in form, being sometimes transversely 

 oval, the beaks much nearer the anterior margin, the posterior side 

 more compressed, the cardinal margin straighter and less angular, 

 than in the typical form. 



This shell appears to be distinguished from C. Bellovacina, 

 Deshayes, by the posterior margin being shorter and less angular, and 

 the general form being more orbicular and symmetrical. 



Heme Bay. Mr. Edwards's Collection. 



AsTARTE TENERA, u. sp. Plate XVI. fig. 6. 



Testa subtrigona, depressa, tenera, insequilaterali, conc'entrice irregulariter rugosa ; 

 latere postico compressiusculo ; umbonibus submedianis ; lunula ovata, profunda, 

 laevigata ; marginibus crenulatis. 



A somewhat trigonal and rather fragile shell ; the posterior side 

 being slightly compressed and angulated ; the surface marked with 

 concentric symmetrical ribs and intervening furrows in the young state, 

 which become irregular both in form and distance in the adult shell, 

 giving it a rugose appearance ; the intermediate furrows are faintly 



