112 The Ottawa Naturalist. [Sept. 



Anterior portion of each valve short, and comparatively 

 broadly rounded; posterior moiety of the same longer, mode- 

 rately produced, narrowing rapidly both above and below, and 

 bluntly pointed at its extremity; ventral margin forming a 

 longitudinally semiovate curve; superior border descending 

 rapidly in front of the beaks, and rather more gradually so behind 

 them; umbones broad and prominent; beaks incurved and 

 placed at a short distance from the anterior end. 



Test unknown; surface of casts of the interior smooth. 

 Hinge dentition also unknown. Anterior muscular scar deeply 

 impressed and concentrically striated; posterior scar indistinctly 

 defined, apparently narrowly subovate and acutely pointed 

 above. 



Three casts of the interior of single valves, two of which 

 are figured, and one cast of the two valves united. 



SowTERiA, gen. nov. 



Shell rather small, equivalve, moderately convex, some- 

 times tumid and always most prominent on the oblique posterior 

 umbonal slope; subtrapezoidal in marginal outline, a little 

 longer than high, and very inequilateral. Posterior area defined 

 by an abrupt inflection of each valve at and behind the sub- 

 angular umbonal declivity. 



Test unknown; in casts of the interior the greater part of 

 the surface is marked by a few large concentric rib-like folds, 

 but the posterior area of both valves is nearly or quite smooth. 

 Hinge dentition and muscular impressions unknown. 



Type and only known species of the genus, Whitella Cana- 

 densis, Raymond. 



All the specimens of W. Canadensis that have yet been 

 collected show only the general shape of the shell and its coarser 

 surface markings. These, however, are so peculiar as to be 

 readily distinctive. The reference of these shells to the genus 

 Whitella can scarcely be regarded as satisfactory, and the 

 writer would prefer to regard them as more probably indicative 

 of a new generic type, whose precise affinities have yet to be 

 ascertained, and for which the name Soivteria is here provisionally 

 suggested. 



SowTERiA Canadensis (Raymond). 



Plate III, figs. 13, 14 and 15. 



Whitella canadensis, Raymond. 1905. Amer. Journ. Sci., Fourth 

 Series, Vol. XX, p. 373. 



The cotypes of this species are casts of the interior of two 

 detached left valves from the Chazy sandstone at Aylmer, Que., 



