Silurian Fossils 
63 
part to produce, in conjunction with the flat ventral side, a sub- 
triangular cross-section. The ventral side, although strongly flat- 
tened, is slightly convex, and bears indications, along the median 
part, of two or three faintly defined linear, longitudinal ridges. 
A shallow groove, less than a millimeter from the lateral margins, 
gives these margins a more acute cross-section. The specimens 
are chiefly in the form of casts of the interiors, or, at least, do not 
preserve the test well. The larger specimen, however, preserves 
distinct traces, on the dorsal side, of numerous, close-set, longi- 
tudinal striations, alternating in size. Judging from Hyolithus 
newsomensis, these longitudinal striations may have been absent 
from the ventral side. 
Osgood bed: Clifton, Tennessee. 
Hyolithus newsomensis. 
{Plate I, Figs, j A, B.) 
Length, 22 to 25 mm.; width at larger end, 5.5 mm.; vertical 
diameter at right angles to the width, 4.2 mm. Dorsal side evenly 
convex, in cross-section approximately semicircular. Ventral side 
flattened, the median parts distinctly though moderately concave. 
Dorsal side striated lengthwise, about 5 or 6 more prominent 
striae in a width of 2 mm., the intervals occupied by 4 to 8 finer 
ones; crossed by transverse striae which are difficult to see even 
with a lens. Ventral side crossed by fine transverse striae and lines 
of growth, and by almost imperceptible longitudinal striae. Judg- 
ing from the transverse striae, the aperture was not oblique but 
opened approximately at right angles to the length of the shell. 
Waldron bed: Newsom, at the old quarries half a mile south of 
the station; Swallow bluff, along the upper part of the bluff south 
of the landing; Iron City, along the top of the bluff' at the station; 
all in Tennessee. 
Diaphorostoma cliftonensis, sp. nov. 
{Plate III, Figs. 41 A, B.) 
This species has usually been referred to Diaphorostoma niag- 
arense, to which it evidently is closely related. However, it is not 
identical, and the failure to distinguish between the two species 
gives them little value in determining the horizons of the rocks in 
which they are found. Diaphorostoma niagarense occurs typically 
