Strophomena and Other Fossils 
37 
appears with the close of the Lexington limestone, and is not seen 
again until the close of the Arnheim, where it is represented by 
Strophomena concordensis. In the Waynesville and Liberty beds, 
it is represented by Strophomena planumbona and its many varie- 
ties; and Strophomena vetusta, from the Liberty and Whitewater 
beds, probably is a variation from the same phylum. 
Strophomena higginsportensis^ sp. nov. 
{Plate II, Figs. 3 A, B; Plate X, Fig. 4) 
Only the interior of three pedicel valves is known. From these 
interiors it is evident that the exterior of the pedicel valve is 
comparatively flat. There is a moderate convexity toward the 
beak, but anteriorly and laterally the valve is flat rather than con- 
cave. The generic relations of the valves is indicated by the mus- 
cular area and the hinge-area. In one of the valves from Stony 
Point, on the Ohio River, in Bracken county, east of Higginsport, 
the hinge-area has a height of almost 2 mm., the width of the valve 
being 30 mm. and the length 20 mm. The sides of the delthyrium 
diverge at an angle of 85 degrees. The deltidium is convex, 
and the teeth extend scarcely a millimeter beyond the hinge- 
line. They are supported by flat, vertical, thin dental plates, 
which extend diagonally forward in the same direction as the sides 
of the delthyrium, decreasing in height rapidly from the anterior 
termination of the teeth to a point about 2J mm. beyond the edge of 
the hinge-area, defining the posterior parts of the muscular area . 
From the anterior termination of these dental plates a very low 
ridge extends forward, limiting the sides of the muscular area. The 
two ridges are scarcely 3 mm. long; they are slightly convergent 
toward the front, and at a distance of 5 mm. from the hinge-area, 
measured vertically, they become imperceptible. The greatest 
width of the hinge-area is scarcely 6 mm. Anteriorly, the limits of 
the area are not defined. Excepting in the immediate vicinity of 
the muscular area, where the shell is smooth, the interior is radi- 
ately striated, the shell substance being very thin and plainly indi- 
cating the striation on the exterior surface. There are about 15 
striae in a width of 5 mm., varying in a second specimen to 19 in a 
width of 5 mm. A specimen from Ivor, Kentucky, 30 mm, wide 
and 20 mm., long, presents 12 radiating striae in the same width. 
