302 



and front uniformly rounded ; area large, its height sometimes equal to 

 its -width, striated parallel to the hinge line, usually a little concave, some- 

 times at a right angle to the plane of the margin, but often sloping a little 

 backwards ; foramen large, apparently open, and about one-third the 

 whole width. Dorsal valve moderately convex. Surface with fine, sharp 

 rugose strine, and a few concentric sub-squamose hnes. 



The form of the dorsal valve is usually semicircular, the front margin 

 shewing some traces of a wide, shallow sinus. The proportional length 

 and width, however, varies to a small extent. 



Width on the hinge line about 2 lines ; length about 1 line. 



Locality and Formation. — Point L^vis, limestone No. 1 ; Quebec 

 group. 



Collector.— "I^. C. Weston. 



Orthis Corinna. (N. sp.) 



Fig. 292. 



Description. — Small , transversely oblong or ovate ; hinge line equal to, 

 or a little less than, the greatest width ; cardinal angles either rounded or 

 rectangular. Ventral valve rather convex, most elevated near the beak, 

 usually flat or concave from the beak to the cardinal angles, a wide, shal- 

 low sinus from the front margin upwards, which dies out before reaching 

 the umbo. The beak appears to be a little depressed below the umbo, 

 but it is not preserved in the specimens observed. Area wide, flat, sloping 

 a little backwards. Dorsal valve moderately convex, with an obscure fold 

 in the front half. Surface with very fine radiating striiie, six to nine in 

 the width of one line. 



Width from 5 to 6 lines ; length varying from two-thirds to thrce- 

 fuurths the Avidth. 



The sides in the upper half are sometimes straight and parallel, and 

 sometimes rounded. Anterior angles rounded. The front margin is 

 usually straight, or a little concave, in the middle. 



Locality and Formation. — Stanbridge, range G, lot 20 ; Quebec group. 



Collector.— T. C. Weston. 



