Mr. T. K. Jones on some species of Leperditia. 89 



tubercle distinct, especially in the casts; central tubeixlc not 

 distinct. 



The anterior and posterior borders of the right valve present a 

 slight marginal rim, especially in the younger specimens. A 

 distinct but very narrow marginal rim is seen on the anterior, 

 ventral, and posterior borders of some young left valves. The 

 ventral margin of the right valve is thick and incurved, over- 

 lapping that of the opposite valve, which has its inner edge in- 

 verted at a somewhat acute angle ; this inverted ventral plate is 

 smooth. 



Prof. Hall's figures, which he refers with doubt to " C. alia," 

 agree in general contour with the form under notice ; but the 

 unworn surface of the latter is not papillose like the Schoharie 

 specimens. Mr. Vanuxem's figures are wretched; but as Prof. 

 Ilall appears, after having examined specimens of the fossil 

 indicated by Conrad and Vanuxem, to be disinclined to separate 

 the two, it is quite possible that all may be referred to one 

 species. Mr. Conrad * and Mr. Vanuxem quote the species as 

 occurring in the Tentaculite limestone of the Waterlime group ; 

 Prof. HalFs specimens came from the Coralline limestone of 

 Schoharie. 



The Arctic specimens which I have here referred to Leperditia 

 alta, although they differ in form less from L. Balthica than from 

 L. Arctica, still do not present the characteristic obliquely-sub- 

 oval outline of the former, but, the larger individuals at least, 

 have a subglobose shape. Their marginal rim, though slight, 

 is also a good distinctive character. In size they occasionally 

 equal L. Arctica, but do not approach the magnitude of the 

 Gothland specimens. 



4. Leperditia Britannica, Renault (?). PI. VI. figs. 6 & 7. 



Rouault, Bullet. Soc. Geol. France, deux. ser. 1851, vol. vnii. 

 p. 377, woodcut figs. 1, 2, 3. 



Dimensions : — 



Length. Breadth. 

 (inch) (inch) 



h\ 2¥ (about). Bretagne specimen. 



i| /^ Normandy specimen : right valve. 



2T 2T Normandy specimen : right valve. 



An odd dextral valve, apparently referable to the species in- 

 dicated above, affords the following characters. 



* Under the name of" Cytherina fabulites," Mr. Conrad has described 

 (Phihul. Acad. Nat. Sc. Proceed, vol. i. p. 332) a bivalve Entomo^tracan 

 from the Trenton limestone of Mineral Point, Wisconsin, which from the 

 ilescription of its shajMi and size is probably a Leperditia. 



