71 
three folds radiating from the beak and the pedicle valve has two distinct 
folds bounding the median sinus, whereas in our shell, as in A. angelica , 
the sinus is depressed. A . angelica , as defined by Hall, is made to include 
both broad forms like ours and narrow, more elongate ones, though the 
original description applied only to the latter type with length greater 
than width, in the proportion of seven to six, respectively; this propor- 
tionately longer shell was due to the greater length of the umbonal region 
of the pedicle valve. Aside from the fact that our specimens are confined 
to the broad form with short umbonal region, they agree closely with A. 
angelica as described by Hall 1 . 
Locality and Horizon. In the Upper Devonian of the Appalachian re- 
gion and Nevada. In the Minnewanka region in the Upper Devonian of 
sections 2-38 (c); 4-5 (R). 
Genus, Cleiothyridina Backman 
Cleiothyridina parvirostris (Meek and Worthen) 
1860. Athyris parvirostris Meek and Worthen, Proc. Acad. Nat, Sci. Phil., 
p. 451; A. planosulcataf Meek and Worthen, 1866, Geol. Surv., 
111., vol. 2, p. 254, PL 18, figs. 8 a-d; Cleiothyridina parvirostris Weller, 
1914, Geol. Surv., 111., Mon. 1, p. 481, PI. 78, fig. 25, PL 80, figs. 
61-66. 
Remarks. Our form is apparently identical with the Mississippi 
Valley species. 
Locality and Horizon. The Lower Mississippian of Mississippi valley. 
In the Minnewanka region in the Lower Mississippian of sections 2-23 (r), 
25 (r). 
Cleiothyridina lata n. sp. 
Plate IV, figure 1 a, b, c 
Shell of medium size, transversely subelliptical in outline, greatest 
width near mid-length of the shell. Dimensions of a nearly complete 
mature shell are: length of pedicle valve 25 mm.; of brachial valve 23 mm.; 
width 31 mm.; thickness of conjoined valves 15 mm.; length of hinge-line 
15 mm. Valves subequally convex. Cardinal extremities rounded. 
Pedicle valve most convex in umbonal region. A faint median 
flattening is present at the umbo; this beyond the middle of the shell 
develops into a broad median sinus and remains shallow to the anterior 
margin of the valve. Beak rather narrow, incurved, truncated by a 
moderately large foramen. Internally, strong dental lamellsB extend 
about one-third the distance to the anterior margin. 
Brachial valve most convex in the umbonal region. A median 
elevation corresponding to the median sinus of the opposite valve is de- 
veloped, its sides merging imperceptibly into the general surface of the 
valve, except at the anterior margin where it becomes definitely a fold. 
Surface of both valves covered with numerous, narrow, concentric 
ridges which are covered with minute spines. Both ridges and spines 
are destroyed upon slight exfoliation. 
1 Pal., New York, vol. 4. 
