342 Annals of the Carnegie Museum. 



limestone on the road running from Montreal Road to the Ottawa 

 River, three miles east of Ottawa, where there is an outcrop of white 

 sandstone by the roadside. The spec es also occurs in the limestone 

 of the Pamelia all around Ottawa. 



23. Sowteria canadensis (Raymond). (Plate XXIX, figures 12, 13). 



Whitella canadensis Raymond, American Joiirnal of Science (Ser. 4), Vol. XX, 



1905. P- 373- 

 Sowteria canadensis Whiteaves, Ottawa Naturalist, Vol. XXII, 1908, p. 112, PI. 3, 

 figs. 13-15- 

 Whiteaves's description of the genus is as follows: 

 Shell rather small, equivalve, moderate'y 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 subangular 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 denti- 

 tion and muscular impressions unknown." 



Specific Characters. 



"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 mid-height; 

 posterior portion moderately 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." 



Locality. — Rather common in the sandstone of the Pamelia at 

 Aylmer, near Wright's brickyard above Tetreauville, and at the same 

 locality east of Ottawa as Cyrtodonta breviiiscnla. 



EXPLANATION OF PLATES. 

 Plate XXIX. 



1. Ctenodonta peraciita Raymond. A small, imperfect, but free, right valve, 

 X4. 



2. The same specimen, exterior view, X 4. 



3. The same specimen, a photograph of the interior. 



4. 5. Ctenodonta ? bidorsata Raymond. Two specimens. Natural size. 



