392 Capt. T. Brown on some new sjiecies of the genus Pachyodon. 



nearly parallel ; anterior side short and rounded ; posterior side 

 elongate, and obliquely subtru^ncate from the hinge line, termi- 

 nating below in a short, slightly acuminated cm-ve ; sm'face 

 rather smooth, with a few, distant, transverse, shallow grooves. 

 Ironstone shale at Low Moore, Yorkshire. 



7. Pachyodon Dawsoni. PI. XV. fig. 10. 



Orbicular ; umbones central, large, produced and remote ; sur- 

 face nearly smooth, with only a few nearly obsolete concentric 

 wrinkles ; thickness equal to more than half its diameter. 



Found in the ii-onstone shale at Low Moore near Bradford, 

 and is in the cabinet of Mr. S. Gibson. 



8. Pachyodon nanus. PI. XVL fig. 1. 



Smooth, posterior side elongated and obliquely subtruncate 

 above, subacute below, anterior side rounded; umbones pro- 

 duced and rounded ; hinge line arcuated. 



Coal shale at Middleton, near Leeds. 



9. Pachyodon Rhindii. PI. XVL fig. 2. 



Subacute at both extremities ; basal line considerably arcuated, 

 rather produced opposite the umbones ; posterior side turned 

 slightly upwards ; umbones subcentral, prominent, and very 

 close ; hinge line cm'ved ; sm-face with transverse, shallow, irre- 

 gular wrinkles. Length equal to two-thirds of its breadth. 



Coal shale, Polmont, Stnlingshire. 



10. Pachyodon Amygdala. PL XVL fig. 3. 



Inflated, anterior side rounded; posterior side acuminated, 

 with an acute beak-like termination ; umbones rather obtuse and 

 remote ; basal line considerably arcuated ; sm-face with many 

 irregular acute ^\Tinkles. 



Ironstone shale, Low Moore, Yorkshire. 



11. Pachyodon exoletus. PL XVI. fig. 4. 



Shell transversely elongate, its breadth about double its length ; 

 sm-face quite smooth ; umbones blunt, placed near to the anterior 

 side, which is round ; posterior side acuminated and subacute ; 

 hinge line slightly arcuated, basal line nearly parallel ; thickness 

 somewhat more than half its length. 



Ironstone shale. Low Moore, near Bradford. 



12. Pachyodon dubius. PL XVI. fig. 5. 



Subovate, both sides rounded; umbones slightly produced 

 and rounded ; hinge and basal lines arcuated ; surface with nearly 

 obsolete, irregular, concentric wrinkles. 



Coal shale near Newcastle-on-Tyne. 



