83 



of the lateral margin an angle of about 130°; foramen about as wide as 

 high. Dorsal valve moderately convex, largely compressed at the cardinal 

 angles, a wide, shallow mesial sinus extending to the beak ; umbo incon- 

 spicuous ; foramen wide, triangular, and without a divaricator process ; area 

 almost linear, lying nearly in the plane of the lateral margin. Surface 

 with fine bifurcating ribs, 4 or 5 m the width of one line, with usually a 

 much finer one between each two of the larger. 



Width 5 lines ; length 3 lines. 



This species is much broader than 0. Mectra, and has the dorsal valve 

 more convex. 



Locality and Formation. — Point Levis ; in the upper part of limestone 

 No. 2, Quebec group. 



Collectors. — Sir W. E. Logan, J. Richardson. 



Orthis Eudocia. (N. sp.) 



Fig. 76. a, b, c. 



Description. — Semi-oval ; hmge-line equal to the greatest width of the 

 shell ; cardinal angles apparently rectangular ; sides somewhat straight, 

 and sub-parallel for two-thirds the length ; front angles and margin 

 uniformly rounded. Ventral valve gently convex ; greatest height in the 

 upper half, sloping with a slightly convex descent to the sides and front 

 margin ; beak nearly of the same height as the shell, very shghtly 

 depressed ; area moderate, flat, extending to the cardinal angles, forming 

 with the plane of the lateral margins an obtuse angle of about 120° ; 

 foramen large, extending to the beak. Dorsal valve flat, with a sUght 

 concavity in front of the beak, along the middle. Surface with fine striae 

 of unequal size, about 8 in the width of one line, at the front margin ; of 

 these, usually about three are much stronger than the others. 



Width 8 lines ; length of ventral valve 7 lines ; height of area at the 

 beak li fines. The doi'sal valve is a little shorter than the ventral. 



Closely allied to 0. tricenaria, from which it difiers only in having the 

 ventral valve less elevated, and the sm-face finely striated, instead of 

 coarsely ribbed. 



Locality and Formation. — Point L^vis ; in the upper part of limestone 

 No. 2, Quebec group. 



Collectors. — Sir W. E. Logan, J. Richardson. 



