75 
Genus, Bakewellia King 
Bakewellia parva Meek and Hayden 
1858. Bakewellia parva Meek and Hayden, Trans. Albany Inst., vol. 4, 
p. 78; White, 1877, U.S. Geog. Surv., W. 100th Mer., vol. 4, 
p. 153, PI. 11, figs. 7 a, b. 
Remarks . Only left valves are in this collection and these agree in 
every particular with those described and figured by Meek and Hayden 
from New Mexico and Arizona, except that they are slightly larger. There 
are indications of two or three denticulations beneath the beak, but it is 
impossible to be sure of them on account of the coarse sandstone in which 
the shells are preserved, and on account of the entire disappearance of the 
shell substance. 
Locality and Horizon. Pennsylvanian of Kansas, New Mexico, 
and Arizona; Permian of Kansas, Arizona, and Nevada. In the Minne- 
wanka region in the Permian of section 1-14 (c). 
Genus, Myalina de Koninck 
Myalina mississippiensis n. sp. 
Plate IV, figures 2, 3, 4, 5, 6, 7 
1903. Myalina keokuk Girty, U.S. Geol. Surv., Prof. Paper 16, p. 309, 
PI. 1, fig. 12. 
Description. Small, subquadrate, oblique. Hinge straight and 
equalling the greatest width of the body part of the shell. Length of 
hinge of a mature specimen 15 mm. ; oblique length of shell, from beak to 
postero-ventral margin, 20 mm. Anterior and cardinal margins con- 
verging at an angle of about 65 degrees. Umbonal and body part com- 
pressed, much elevated and rather sharply delimited throughout its entire 
length from the large, flattened, posterior wing. Beak small, compressed, 
curved slightly anteriorly; its anterior slope is very steep, its posterior 
more gentle. A very small anterior ear is present. 
Surface marked by regular concentric lamellae from beak to basal 
margin and by fine, concentric growth lines. 
Remarks. There are few species of this genus as small as this. It is 
likewise distinguished by its convexity and by its regular concentric lam- 
ellae. In most respects except size it closely resembles M. keokuk of Mis- 
sissippi valley. 1 An average specimen of that species is stated to measure 
2-2 inches by 1*25 inches. The present species likewise closely resembles 
M. sanctiludovici of the Keokuk of Illinois to Missouri, 2 but differs in its 
much more convex body part. Myalina orthonota Mather, described 
from the Morrow group (Mississippian-Pennsylvanian transitional) of 
Arkansas and Oklahoma 3 agrees closely in size, but with its shorter, more 
oblique hinge-line and less definite posterior wing, finds its closest affinities 
with the M. perattenuata type of shell and not with M. keokuk. It would 
seem that the specimen identified doubtfully as M. keokuk by Girty from 
the Ouray limestone of Colorado 4 may be included with the Minnewanka 
species. Girty records dissatisfaction in its identification since his one 
specimen was much smaller than is typical of M. keokuk, though it is some- 
what larger (oblique length 32 mm.) than is our normal type. 
i~Geol. Surv. .111., vol. «, PI. 30, fig, 5 . 
* Geol. Surv.. 111., vol. 5, PI. 22, fig. 3. 
* Bull. Sci. Lab. Denison Univ. , vol. 18, p. 221, PI. 15, fig. 4. 
4 Loc.cit. 
