296 CONTRIBUTIONS TO CANADIAN PALEONTOLOGY. 



species was mainly based would, if perfect, have slightly exceeded seven 

 inches in length. 



(S.) MODIOMORPHA COMPRESSA. (N. Sp.) 



Plate 38, figs. 8 and 9. 



Shell subelliptical, moderately elongated, nearly twice as long as high, 

 and very inequilateral : valves strongly compressed laterally, very gently 

 convex, and most prominent on the oblicjue posterior umbonal slope of 

 each valve, and broadly but shallowly depressed in front of these slopes. 

 Anterior side short and narrowly rounded : posterior side much longei- 

 than the anterior, its outer margin obliquely truncated above and nar- 

 rowly rounded below ■ dorsal margin nearly straight or very gently con- 

 vex, ascending slightly behind and ultimately forming an obtuse!}' suban- 

 gular junction with the posterior end : ventral margin nearly straight 

 and faintly concave in the centre in some specimens, but somewhat con- 

 vex in others . umbones broad, compressed and depressed : beaks curved 

 inward and forward, placed very near to the anterior end, but not quite 

 terming,!. 



Surface markings not satisfactorily shown, all the specimens collected 

 being mere casts of the interior of the valves. A small portion of the 

 test, which happens to be still adherent to the posterior end of one of 

 these casts (fig. 8) is, however, marked by two or three concentric raised 

 lines. Anterior muscular impression nearly circular, comparatively large, 

 and situated close to the anterior margin. Pallial line distinctly impressed, 

 entii'e and parallel to the ventral margin. Posterior muscular impression 

 and characters of the hinge dentition unknown. 



The specimens are all too imperfect to admit of an accurate statement 

 of their dimensions, but both of the figures are of natural size. 



Shores of Dawson Bay, Lake Winnipegosis, at Whiteaves Point (three 

 specimens), and aVjout two miles east of Salt Point (two specimens) ; J. 

 B. Tyrrell, 1889. 



This shell has much the same lateral outline as the J/, altifoniie of 

 Walcott*, from the Lower Devonian of Nevada, but the former is strongly 

 compressed at the sides and the latter as strongly convex. 



MODIOMORPIIA TUMIDA. (N. Sp.) 



Plate 38, figs. 10 and 10 a.) 



Shell of medium size, ovately subelliptical, rather less than twice as 

 long as high, and highest a little behind the midlength : valves tumid and 



''Palseont. Eureka distr. Nevada, 1.S84, p. 161), pi. v., fig. !). 



