9 



Description. — Hinge-line straight, a little less than the greatest width 

 of the shell ; sides straight or slightly convex for about one half the 

 length ; anterior angles obtusely rounded ; front margin either uniformly 

 convex or with a small portion in the middle somewhat straight. Great- 

 est width a little in front of the middle. Ventral valve strongly and uni- 

 formly convex, most tumid about the middle ; beak depressed below the 

 greatest convexity of the shell ; cardinal edges straight or gently concave, 

 diverging from the beak at an obtuse angle. Area unknown. Dorsal 

 valve somewhat flat, most elevated at the beak, in front of which, along 

 the middle of the shell, there is a wide shallow concavity extending to the 

 front margin ; on each side of the beak, descending with a somewhat flat 

 slope to the cardinal angles ; area unknown, apparently half the height of 

 the ventral area and nearly at right angles to the plane of the margin. 

 Beak erect, obtusely pointed, forming the most elevated part of the shell. 

 Surface with strong concentric sub-lamellose ridges which do not converge 

 to the beak but terminate on the cardinal edges, their course conforming 

 to the margin of the shell. Four or five ridges in the width of one line. 



Length of largest dorsal valve seen GJ lines, greatest width 8 lines. 

 Length of largest ventral valve in a straight line from back to front 

 7 lines, width 10 lines. The proportional length and width appear to 

 vary. The apical angle of the ventral valve also varies, being in some 

 specimens much more pointed at the beak than in the one above figured. 

 Specimens of all sizes occur from 3 lines in width upwards.* 



Locality and Formation- — Anse au Loup, on the north shore of the 

 Straits of Belle Isle. In limestone of the Potsdam group. 



Also abundantly in the condition of casts li mile east of Swanton in 

 Vermont. 



Collectors. — J. Richardson, Dr. G. M. Hall, and Rev. J. B. Perry. 



* Since the above was written, I have examined many casts of the interior of this 

 species, and am inclined to the opinion that it is generically distinct from Oholdla 

 chromatica. From the very considerable elevation of the beali the dorsal valve must 

 have an area and prolpably a foramen. In one specimen there are two large oval 

 impressions faintly impressed, but still distinctly visible. There is no trace of the 

 lateral scars ; and the form, notwithstanding the characters of the surface, conveys the 

 idea of an Oithisina. Bhould, upon further esamination, my suspicions turn out to be 

 well founded, I shall call the genus Kutoi!GIna, afler the celebrated European naturalist, 

 KuTORSA. It is not quite certain which is the ventral or which the dorsal valve. 



