waurr.| CRETACEOUS FOSSILS. 17 
distinct in each valve. A few fragments show the surface to have been 
marked by the ordinary concentric lines of growth, and also that the 
test, although firm, was not massive. 
The dimensions cannot be definitely given, but the largest example 
discovered indicates a length of at least 80 millimeters. 
This shell differs too much from any of the few known Cretaceous spe- 
cies of the genus to need detailed comparison, but it is related to G. sub- 
tortuosa Meek & Hayden, which it resembles in being tortuous., It 
differs, however, from that species in being a proportionally much shorter 
shell, in the shape and position of the adductor scars, and in the relative 
position and arrangement of the cartilage-pits. It is less tortuous than 
G. tortwosa Sowerby, and its proportions are different. 
Position and locality—Strata of the Dakota Group, Saline County, 
Kansas, where it was discovered, associated with the preceding species, 
by Prof. B. I’. Mudge, in whose honor the specific name is given. 
Genus PINNA Linneus. 
PINNA LAKESII White. 
Plate 11, figs. 1 a and D. 
_ Pinna lakesti White, 1879. An. Rep. U.S. Geol. Sur. Terr. for 1877, p. 181. 
Compare with Pinna restituta Heeninghaus. 
Shell rather large, slender anteriorly but beeoming quite broad ae 
somewhat compressed posteriorly; sides not angular or otherwise con- 
spicuously marked along the median line, nor very convex except near 
the anterior end, where the transverse thickness of the shellis about 
equal to its height from base to dorsal border; dorsal margin broadly 
concave from front to rear and longer than the basal margin ; posterior 
border convex, or rather truncated obliquely downward and a little back- 
ward from the dorsal border toa point a little below the median line, where 
it is abruptly rounded, and, by a long forward slope, blends with the basal 
border, which border is slightly convex or nearly straight. Surface 
marked by the usual lines of growth and by some concentric wrinkles, 
which latter are more distinct below than above the median line. It is 
further marked by numerous slender, slightly raised, radiating ribs, 
which extend continuously from the anterior to the posterior end of the 
shell. Seven or eight of these ribs mark the whole space above the 
median line, and three or four are seen below it, leaving the lower half 
of the space below the median line free from ribs. The ribs are merely 
close-set raised lines upon the narrow front end of the shell but become 
stronger farther backward. They are there much narrower than the 
intervening spaces, because the width of the latter increases posteriorly 
much more rapidly than that of the ribs. 
Full length of the specimen figured on plate 11, about 280 millimeters ; 
width (vertical) of the same at the widest part, about 83 millimeters. 
This species is in no danger of being coufounded with any other 
described and figured form from American rocks, but it somewhat re- 
sembles the P. decussata Hoeninghaus as figured by Goldfuss. It differs 
from that species, however, by increasing more rapidly in size from front 
to rear, by the much less convexity of its basal margin, and by the char- 
acter and direction of the posterior and postero-basal borders as de- 
scribed above. 
Position and locality.—No examples of this species have been satisfac- 
torily identified from any other region than that of Northern Colorado, 
Pagal 
