558 CLINTON R. STAUFFER 
margin and partially bisected by a prominent rounded ridge impres- 
sion. ‘This latter was apparently longitudinally striated while the 
muscular scars themselves were concentrically marked. 
Horizon and locality.—Amherstburg dolomite, Stony Island Dry 
Cut, Livingston Channel, Detroit River, near Trenton, Michigan. 
Stropheodonta delicatula n.sp. 
PLATE II, Fics. 4 AND 6 
Shell semi-elliptical, somewhat wider than long. Cardinal 
extremities produced, hinge line usually greater than the greatest 
width of the shell. 
The specimens found are chiefly brachial valves and of those 
only the external impression, with rarely a rather poor preservation 
of the shell. Fragments of the pedicle valve show that it was 
regularly convex and rather gibbous. The beak was small and 
slightly incurved and extending beyond the area as in Stropheodonta 
demissa. Brachial valve moderately to deeply concave, usually 
following rather closely the inside curvature of the pedicle valve, 
leaving scarcely a sixteenth of an inch as the probable thickness 
of the animal. 
Area of pedicle valve arcuate and more or less triangular; area 
of the brachial valve apparently flat and uniform in width. 
Surface of valves marked by strong radiating striae, rather dis- 
tantly spaced, and between which are numerous fine striae. Jn 
the umbonal region the surface is marked by distinct ribs or costae, 
which seem to persist for half an inch or more from the beak and 
then are gradually lost. These radiating surface ornamentations 
are crossed by numerous growth lines which are occasionally 
aggregated into more conspicuous wrinkles. This species may be 
compared with Siropheodontia galatea. 
Horizon and locality.—Amherstburg dolomite, Stony Island 
Dry Cut, in Livingston Channel, Detroit River, near Trenton, 
Michigan. 
Nucleospira livingstonensis n.sp. 
leapNauiay JUL oe "(6) 
Shell nearly circular in outline, rather gibbous and rounded 
oval in transverse section. Width and length nearly equal. 
