434 Mr. J. W. Kirkby on Permian Entomostraca 



posteriorly. Anterior extremity subangulate. Posterior extre- 

 mity somewhat produced^ bluntly pointed. Lateral contour len- 

 ticular; greatest diameter central, rather more than one-fourth 

 of the length. Hinge with the left valve overlapping the right 

 evenly along the dorsal margin. Flange of left ventral margin 

 posteriorly situate. 



Very rare in the fossiliferous limestone of Tunstall Hill. 



Besides the species of Bairdia already noticed, there appear 

 to be one or two additional forms belonging to the fauna of the 

 fossiliferous limestone, which may subsequently be established 

 as species. Specimens have occurred that seem to imply this 

 idea ; but, owing to a paucity of materials, and, in some cases, to 

 an apparent affinity to described species, I have not ventured to 

 specialize them. There was one well-marked individual, of tri- 

 angular contour, which was unfortunately lost after it had been 

 outlined, and which I have little doubt was the Cy there acuta of 

 Jones. It was minute and exceedingly globose; the ventral 

 margin almost straight, and the dorsal margin convex; the 

 extremities acute and similar. 



Leperditia ? Permiana, Jones. Plate XI. figs. 5-13. 



Syn. Dithyrocaris Permiana, Jones, Mon. Perm. Foss. p. 66. tab. 18. fig-. 1. 

 Ceratiocarisl Permiana, Jones, Morris's Cat. Brit. Foss. 2n(i edition, 

 1854, p. 103. 



Length ^^^ inch ; height ^^j inch. 



Carapace oblong-ovate, ark-shaped, equivalve, very convex ; 

 valves thick. Dorsal margin straight, bounded laterally by llat- 

 tish, slightly inclined areas formed by the depression of the 

 upper region of the valves. Ventral margin straight centrally, 

 or very slightly sinuate. Anterior extremity angulate at its 

 junction with the dorsal margin, and bluntly rounded ventrally : 

 the dorsal angle is sometimes the most prominent ; at others a 

 point midway between the margins protrudes most. Posterior 

 extremity angulate dorsally, more pointed than the former, the 

 antero-dorsal angle being more projecting, from which a convex 

 line slopes gradually to the ventral margin. From the extreme 

 points of the dorsal margin of each valve proceed two strongly 

 produced rims, or marginal expansions, which become more widely 

 separate as they approach the ventral margin. The innermost rim 

 (of single valve) is elevated, and forms a raised retlexed edge 

 round the middle portion of the valve. The outermost or most 

 ventral rim is not reflexed, but projects at a right angle from the 

 ventral portion of the valve ; along the inner surface of this rim, 

 which forms the contact-margin of the valve, extends a slightly 

 elevated projection, on a plane with the ventral convexity of the 



