LOWER SASKATCHEWAN RIVER VALLEY. 
13 
DESCRIPTION OF SPECIES. 
Leptaena sinuosus n. sp. 
Plate 1, Figures 1-4. 
Shell small, subquadrate, cardinal extremities produced. 
Surface of shell covered with transverse irregularly zigzag 
wrinkles giving a surface comparable with that of a shrivelled 
apple. Toward the cardinal extremities these wrinkles take on 
a semblance of regularity and appear in a limited area as trans- 
verse folds. The surface of each valve is marked by about 
8 or 10 widely spaced slender but sharply defined strise. About 
half of these originate at the beaks, the remainder arising in the 
median part of the shell and extending thence to the front. The 
flat intermediate spaces between these strise in perfectly pre- 
served specimens are occupied by extremely fine strise, but on 
the dolomitic material representing the collection they are sel- 
dom clearly preserved. Margin of valves geniculated in front 
and but slightly or not at all on lateral margins, thus giving a 
sinuous antero-lateral margin with a sinus-like effect at the front 
of the valves. This geniculation in the median portion of the 
anterior margin of the valves is shown in figures 1 and 4. 
The ventral valve is gently convex with a well marked sub- 
circular muscular scar sharply defined at the sides near the hinge 
line by slightly curved dental lamellae, but shallow and indistinct- 
ly defined in front. Anterior margin of valve abruptly bent 
downward producing a sinus-like depression at the front. 
Dorsal valve nearly flat with a geniculated anterior median 
margin. Short, widely diverging teeth extend forward from the 
cardinal area. The character of the geniculated margin which 
is recurved only near the middle of the anterior margin distin- 
guished this shell from L. parvula which is geniculated around the 
entire margin. The peculiar surface markings and small size 
distinguish both this species and L . parvula from other species 
of this genus. 
The types are from the dolomitic limestone outcropping at 
the east end of Cedar lake 2 miles above Cedar Lake P.O. 
(Chemahawin), Manitoba. 
