137 



those figured in the works above cited, but are in every other respect spe- 

 cifically identical. The area varies much in its size and in the amount of 

 its inclination. 



Locality and Formation. — City of Ottawa ; Belleville ; and near 

 L'Orignal. It also occurs at Cmcinnati in Ohio, in the Hudson River 

 group, and at numerous lecalities in Wales, in the Bala group. 



Qollectors.—^\v W. E. Logan, R. Bell, E. BiUings. 



Orthis Maria. (N. sp.) 



Fig. 114. 

 Fig. 114. — Orthis Maria, a, yentral view ; b, side view ; c, view of the front margin. 



Description. — Transversely oblong ; hinge-line equal to or a Httle less 

 than the greatest width ; cardinal angles either rectangular or moderately 

 rounded ; sides gently convex and subparallel ; anterior angles rounded ; 

 front margin with a portion of the middle usually straight. Ventral 

 valve irregularly depressed pyramidal, with a deep rounded mesial sinus 

 which becomes obsolete before reaching the beak ; the lattei> small, 

 pointed, not incurved, scarcely distinct from the cardinal edge, and form- 

 ing the most elevated point of the valve. From the beak to the cardmal 

 angles the shell descends with a flat or sometimes gently concave slope. 

 Area rather large, its height at the beak equal to one eighth of its 

 length, shghtly concave, nearly at a right angle to the plane of the mar- 

 gin, but shghtly overhanging the hinge-line. Dorsal valve rather strongly 

 convex, with its front much elevated in the middle by a large rounded 

 mesial fold which becomes obsolete at the umbo ; cardinal angles com- 

 pressed and shghtly reflected ; umbo large, obtusely rounded, overhang- 

 ing the hinge-luie ; beak very small but distinct, situated on the cardinal 

 edge and not elevated ; area about one third the size of that of the ventral 

 valve, lying nearly in the plane of the margin, slightly concave and some- 

 times a little overhangmg the hinge-line. Foramen of ventral valve tri- 

 angular, its width at base about two thirds the height, apparently open to 

 the beak, but this point not clearly ascertained. Surface with rather fine 

 radiating striae, 3 or 4 in the width of a line at the middle of the front 



