280 The American Geologist. May, i890 
six. Valves rather strongly convex, most prominent near the 
center, where the convexity of one valve equals about one- 
third of the greatest width. Cardinal margin straight, its 
length behind the beaks equal to a little more than half of the 
entire length of shell. Upper half of anterior margin straight 
or faintly concave, forming an angle of about 125° with the 
hinge line. Lower half curving rapidly into the straight basal 
margin, its curve equal to that of the margin in the postero- 
basal region. Upper half of posterior end straight, oblique, 
forming an angle of 130° with the hinge line ; junction between 
the two, obtusely angular. Beaks small, slightly prominent^ 
situated one-seventh of the entire length of shell from the an- 
terior extremity. Umbonal ridge broadly rounded, not a con- 
spicious feature. Cardinal slope flattened. Surface with 
rather strong irregular lines of growth and a few finer concen- 
tric striae. 
Hinge plate narrow, with a long slender posterior tooth. 
Muscular impressions not observed. 
Length, 24.5 mm. ; greatest width in posterior half 15 mm. ; 
hight from base to beaks, 12.7 mm. ; from postero-cardinal an- 
gle to antero-basal margin 19.5 mm. ; from beak to postero-bas- 
al margin 23 mm. ; greatest convexity of single valve 5 mm. 
This species is related to M. tnmcata Hall, but is less high 
posteriorly, and more ventricose. It also has a narrower hinge 
plate and thinner shell, while, the surface markings are also 
somewhat different. 
Position and locality; Lower beds of the Cincinnati group, near 
Cincinnati, Ohio, at an elevation of about 100 ft. above low water mark 
in the Ohio river. 
Modiolopsis alata, n. sp. 
Fig. 8. Modiolopsis alata n. sp., Cincinnati group, Cincinnati, Ohio. 
a, and b, three views of a right valve preserved in shale, c, view of the 
right side of a free cast of the interior showing the small anterior scar. 
The rounding of the postero-cardinal region is probably due to attri- 
tion. 
