Sowteria canadensis
(tiré de l'article de J.F. Whiteaves "Notes on the Pelecypoda or Bivalve Mollusca of the Chazy Formation in Canada,
with Descriptions of One New Genus and Four New Species from the Chazy Sandstone at the Hog's Bay,
near Ottawa". Ottawa Naturalist, vol. XXII(6):112, 113, 1908)
Sowteria, gen. nov.

Shell rather small, equivalve, moderately convex, sometimes 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 Canadensis, 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 Sowteria is here provisionally suggested. 

Sowteria Canadensis (Raymond)

Planche III, figures 13, 14 et 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., collected by Mr. Sowter, and now in the museum of Yale University.  At this locality, numerous casts of right and left valves have been collected by Dr. H.M. Ami and by Mr. Sowter. 

In Mr. Billings' collection of fossils from the Hog's Back there are eleven casts of the interior of single valves of S. Canadensis.  Most of these are imperfect and badly preserved, the three specimens figured on Plate III being the most perfect but by no means the largest.  In figure 14 on that plate the ventral margin is a little restored.  The generic definition of Sowteria is largely based upon these three figured specimens, and the following description of some of their presumably specific characters may be added.  Anterior portion of each valve very short, in some specimens truncated almost vertically at its extremity, in others faintly concave under the beaks above, and rounded at or below the midheight; posterior portion moderately elongated, its extremity obliquely subtruncate above and narrowly rounded below.  Superior border and ventral margin nearly straight or very gently convex; beaks nearly or quite terminal. 

In a right valve of S. Canadensis from Aylmer, collected by Dr. Ami in 1893, there is an oblique, shallow, median depression.