Capt. T. Brown on some new species of the genus Pachyodon. 395 



and remote; anterior side short, nearly straight above, with a 

 cleft termination; posterior side long, with an obliquely sub- 

 truncate termination, point below a little rounded; hinge line 

 very slightly arcuated ; a pretty deep transverse furrow runs close 

 to and nearly parallel with the superior margin on the posterior 

 side ; basal margin with a slight hollow posteriorly ; surface with 

 strong transverse wrinkles, and a few irregular, nearly obsolete, 

 longitudinal furrows, producing an antiquated appearance; 

 thickness f ths of an inch. 



Ironstone shale. Low Moore, near Bradford. 



24. Pachyodon transversm. PI. XVI.* fig. 5. 



Transversely elongated ; umbones blunt and obliquely rounded; 

 anterior side short, rounded and slightly produced at the extre- 

 mity ; posterior side long, gradually declining from the umbones, 

 ending in an obliquely truncate termination, rather acutely beaked 

 below ; hinge line nearly straight, basal line with a slight flexure 

 posteriorly; surface rather smooth. 



Coal shale at Middleton, near Leeds. 



25. Pachyodon hamatus. PI. XVL* fig. 6. 



Oblong-ovate, considerably inflated ; umbones large, produced 

 and slightly inflected ; anterior side rounded, posterior side sub- 

 acute ; hinge line nearly parallel ; basal margin a little arcuated ; 

 surface with strong concentric wrinkles. 



Found by Dr. Fleming in the Oxford clay at Gristhorpe Bay. 



26. Pachyodon vetustus. PI. XVL* fig. 7. 



Transversely elongated, compressed; umbones very obtuse 

 and depressed; anterior side short and subacute; posterior side 

 long, broad, and rounded at the extremity ; hinge and basal lines 

 very slightly arcuated ; external surface with pretty broad, shal- 

 low, concentric wrinkles. 



Found by Dr. Fleming in the carbonaceous shale at Gristhorpe. 



I am strongly inclined to consider this species as belonging to 

 the genus Alasmodon, with which it agrees in all its external 

 characters. 



27. Pachyodon levedensis. PI. XVL* fig. 8. 



Subtriangular wedge-shaped ; umbones rounded, situate con- 

 siderably to one side ; anterior side very short and abruptly de- 

 scending ; posterior side long, acuminated, its superior margin 

 gradually inclining to a truncated termination ; basal margin 

 nearly straight ; surface with transverse antiquated wi'inkles. 



Coal shale at Middleton, near Leeds. 



2E2 



