64} Mr. T. R. Jones on some species of Leperditia. 



perhaps to M. Rouault's species. The British Museum and the 

 Geological Society's Museum contain some highly interesting 

 specimens from Gothland. Mr. Salter has submitted for my 

 examination numerous specimens of Leperditia from the Silurian 

 limestones of the Arctic Regions and elsewhere ; and Mr. Wood- 

 ward and other friends have favoured me with several others. 

 These materials have enabled me to prepare a notice of a few 

 principal forms of the genus, which, though closely related, have 

 sufficient peculiarities of the carapace to render them specifically 

 distinct. 



Class CRUSTACEA. 



Subclass Entomostraca. 



Order Phyllopoda ? 



Family Leperditidje. 



Genus Leperditia, Rouault, 1851. Bullet. Soc. Geol. France, 

 2de serie, tome viii. p. 377. 



Generic characters. — Animal enclosed in a vertical bivalved 

 carapace. Carapace inequivalved ; somewhat resembling a tam- 

 arind-stone and other leguminaceous seeds. Carapace-valves 

 smooth, convex, horny in appearance, nearly oblong, longer 

 than broad*, bean-shaped, inequilateral, posterior half broadest ; 

 dorsal border straight ; ventral border nearly semicircular ; an- 

 terior and posterior borders oblique above, rounded below, the 

 valve-margin passing from each end of the hinge-line in an 

 oblique direction downwards and outwards to about half the 

 breadth of the valve, where it meets the curved ends of the 

 ventral border, and so forms the more or less angular extremities 

 of the valve, the former of which is narrower and sharper than 

 the latter. 



Valves united along their upper (dorsal) borders by a simple 

 linear hinge ; the two extremities of the hinge- border form angles 

 with the anterior and posterior borders in each valve. 



The right valve larger than the left, being broader, and over- 

 lapping completely the ventral border of the opposite valve, and 

 to some extent its anterior and posterior borders. The overlap- 

 ping ventral border of the right valve forms a thick blunt keel 

 to the closed carapace. 



Each valve is somewhat depressed towards the dorsal border ; 

 this border in the left valve is thicker than that of the right, and 

 sometimes slightly overrides it. The ventral margin of the left 

 valve is turned suddenly inwards, forming a thin plate project- 



* The length is measured in the direction of the hinge-hne, — the breadth 

 (or height) in that from the dorsal to the ventral margin. 



