78 



Surface of each valve with from fourteen to eighteen strong undivided 

 ribs separated by deep furrows equal to them (the ribs) in width. 



Width of dorsal valve about 3 lines ; length of the same about 3 lines. 

 Owing to the projection of the umbo, the ventral valve has the length and 

 width more nearly equal. 



The specimens agree so nearly with the figures of 0. calligramma, var. 

 Orthambonites, in the work above cited, that I have no hesitation in refer- 

 ring them to that species. In Russia it occurs in the orthoceratite lime- 

 stone abundantly in the neighbourhood of St. Petersburgh. 



Locality &nd Formation. Point LeVis. In the upper part of lime- 

 stone No. 2, Quebec group. 



Collectors. Sir W. E. Logan, J. Richardson, R. Bell. 



ORTHIS EURYONE. (N. sp.) 



Fig. 71. a, b. 



Description. Shell small, semi-oval ; hinge line equal to the greatest 

 breadth of the shell ; cardinal extremities rectangular or nearly so ; sides 

 straight, gently convex or gently concave, and either parallel for about one 

 fourth the length or slightly converging ; front angles and front margin 

 forming a uniform broadly rounded curve ; a small portion in the middle 

 of the front margin sometimes straight. Ventral valve strongly and uni- 

 formly convex, not carinated along the middle ; a small portion at the car- 

 dinal angles compressed ; umbo large, broadly convex, overhanging the 

 hinge line ; beak very small ; area small, lying nearly in the plane of the 

 lateral margin, hi most specimens rather strongly concave ; foramen narrow, 

 its width less than the height. Surface with from twenty-five to thirty- 

 five small but very distinct ribs. Dorsal valve nearly flat, with a wide 

 shallow mesial sinus extending from the front margin two-thirds the length 

 of the shell. 



Width, 3 lines ; length, 2i lines. 



This species differs from 0. orthambonites in having the ventral valve 

 more broadly convex, and in having nearly double the number of ribs. It is 

 more abundant than that species, and the individuals differ very little from 

 each other either hi size or form. 



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

 No. 2, Quebec group. 



Collectors. Sir W. E. Logan, J. Richardson, R. Bell. 



