14 
MUSEUM BULLETIN NO. 21. 
Leptaena parvula n.sp. 
Plate I, Figures 5-9. 
Shell small, outline as shown in figures 5 to 9. Surface of 
shell irregularly wrinkled throughout. The surface of each valve 
is marked by about eight or more widely spaced slender but sharply 
defined striae, which are well defined only in the anterior half of 
the shell. Extremely fine striae occupy the intermediate spaces 
between these striae, the coarser striae being separated by groups 
of six or eight fine ones. Margin of valves moderately geniculated. 
The geniculation though not very pronounced appears to be 
approximately uniform on the anterior and lateral margins. 
A well marked sub-circular muscular scar sharply defined 
at the sides by slightly curved dental lamellae, but shallow and 
indistinctly defined in front, characterizes the interior of the 
ventral valve. 
Dorsal valve nearly flat with a narrow geniculated margin. 
Cardinal process divided into two small, diverging arms. A low, 
narrow ridge extends forward from the base of the cardinal 
process between the shallow, muscular impressions about one-sixth 
of the distance across the valve. In some specimens this ridge 
is almost or quite obsolete. Short, lateral lamellae extend for- 
ward from the hinge line making acute angles with it. 
Horizon and Locality . — The types are from the dolomitic 
limestone outcropping 8 miles west of Gypsumville. Other 
specimens of this shell which are here figured, have been found 
in the dolomite at the east end of Cedar lake, 2 miles above 
Cedar Lake P.O. (Chemahawin), Manitoba. 
Both occurrences represent the upper part of the Stonewall 
limestone. It is unknown in the lower part of the Saskatchewan 
River section. 
Conchidium decussatum (Whiteaves). 
Plate II, Figures 1-6; Plate III, Figures 1-6; Plate IV, Figures 1-4' 
Pentamerus decussatus Whiteaves, Canadian Record of 
Science, 1891, p. 295, pi. 3, figs. 3, 4. — Calvin, Bull. 
Lab. Nat. Hist. State Univ. Iowa, II, 1892, p. 164, 
pi. 11, figs. 1-3; pi. 12, fig. 2. 
