BIVALVIA. 217 



GASTRANA,* Schum. 1817. 



TELLINA (sp.) Linn. Chemn. 



VENUS (sp.) Retz. 1/88. 



PSAMMOBIA (sp.) Lam. 1818. Turt. 1822. Flem. 1828. 



PETEICOLA (sp.) J. Sow. Lam. 



DIODONTA. Desk. 1845. Forb. and Hani. 1848. Gray, 1851. Woodward, 1854. 



Generic Character. Shell equivalved, inequilateral,' transverse, ovate or subtrigonal, 

 covered with concentric striae or lamellae. Hinge with two teeth in one valve, and 

 one large subbifid tooth in the other. Impressions by the adductors ovate, nearly 

 equal, that by the mantle with a sinus wide and deep. Ligament external. 



Animal with the mantle open, and fimbriated margins ; siphons long, unequal, and 

 separated to their bases, with slightly fringed orifices ; foot linguiform. 



This appears to be a very well marked genus, and strongly characterised by its 

 dentition. A few species only are as yet known either in a recent or fossil state. 

 I have not seen it from any older formation than the Faluns of Touraine. One 

 fossil species has been brought from South Africa, belonging to a tertiary deposit. 



1. GASTRANA LAMINOSA, /. Sowerby. Tab. XXV, fig. 1, a e. 



PETRICOLA LAMINOSA. J. Sow. Min. Conch., t. 573, 1827. 



Nyst. Coq. Foss. de Belg., p. 99, pi. 3, fig. 16, 1844. 



Spec. Char. Testa subirregulari, ovatd vel trigonuld, convexiusculd, clausd, inaqui- 

 laterali ; antice rotundatd, postice anyulatd ; lamellatd, lamellis erectis acutis, striis 

 interstitiis exilioribus ; car dine bidentato ; sinu palliari macjno. 



Shell somewhat irregular, slightly convex, ovate or trigonular, closed, inequilateral ; 

 anterior side rounded, posterior angulated ; covered with sharp and erect concentric 

 ridges or lamellae, and very fine radiating striae between them ; hinge with two teeth, 

 palleal sinus large. 



Length, 2J inches. Height, If inch. 



Locality. Cor. Crag, Ramsholt, Gedgrave, Sutton. 



Red Crag, Sutton, Alderton, Bawdsey, Walton Naze. 



This species is not particularly rare either in the Coralline or in the Red Crag. 

 It has considerable resemblance to Tellinafragilis, Linn. (Petricola oc/iroleuca, Lam.), 

 but appears to differ sufficiently to be removed from that species. Like it, however, it 

 was subject to much distortion ; and though the valves are found free, its habits were 

 probably such as to lead it into confined situations, so as oftentimes to impede the 



* Etym.? ya<m/p, ventral. 



29 



