326 Mr. J. W. Kirkby on Permian Entotnostraca 



It diifers in having the greatest convexity of the dorsal margin 

 posteriorly situate, consequently in possessing an abrupt poste- 

 rior slope and a very gentle anterior depression ; in the blunt 

 but beaked posterior extremity, and in its more compressed 

 lateral contour. 



2. Bairdia ventricosa, u. sp. Plate X. figs. 3 & 3 a. 



Length -^-^ inch ; height -^^ inch. 



Carapace subrhomboidal, ventricose, smooth, rather protu- 

 berant ventrally in anterior half. Dorsal margin flatly convex ; 

 posterior slope abrupt, descending three-fourths of the height, 

 deeply sinuate close to posterior extremity ; anterior slope steep. 

 Ventral margin slightly sinaous, rising rapidly anteriorly. Ante- 

 rior extremity rather acute, the dorsal and ventral margins almost 

 forming a right angle at their juncture. Posterior extremity 

 prolonged into a narrow bluntish point. Lateral contour almost 

 lenticular, ventricose, sinuated anteriorly. Dorsal margin of 

 left valve strongly overlapping that of the right, especially in the 

 centre. The flange of left ventral margin short, situate a little 

 beyond the centre and in posterior half. 



The principal characteristics of this species are its ventricosity, 

 its blunt produced posterior extremity, its angulated anterior 

 extremity, and its slightly sinuous ventral margin. 



It frequently occurred in the fossiliferous limestone of Tun- 

 stall Hill. 



3. Bairdia Reussiana, n. sp. PI. X. figs. 6 & 6 «. 



Length ^^ inch ; height ^j inch. 



Carapace somewhat reniform, flatly convex, smooth. Dorsal 

 margin flatly convex ; posterior slope abrupt, deeply sinuate near 

 its juncture with the ventral margin ; anterior slope gentle. 

 Ventral margin with a deep sinus near the centre, becoming 

 rapidly convex posteriorly; towards posterior extremity margins 

 of valves produced. Anterior extremity rounded. Posterior 

 extremity hQdiktdi. Lateral contour sublenticular, with a flat cen- 

 tral region, slightly concave and pi'oduced posteriorly ; greatest 

 diameter one-fourth of length. Flange of left ventral margin 

 anteriorly situate. Hinge with the left dorsal margin overlapping 

 the right, more so centrally than towards extremities. 



B. Reussiana rather resembles some of the forms oi B.plebeia. 

 I have been induced to separate it from that species on account 

 of its having a sinuate ventral margin, a comparatively blunt 

 and high beak, a less prominent dorsal margin, consequently a 

 greater length compared with its height, and a compressed len- 

 ticular lateral contour. 



