Silurian Fossils 
65 
Platyceras pronum, sp. nov. 
{Plate III, Fig, 40^ 
Shell unguiform, with an ovate outline, the beak being twisted 
sufficiently to make it point toward the right. The shell is striated 
concentrically, but otherwise is smooth. Length, 28 mm.; width, 
18 mm.; vertical elevation, about ii mm. 
Osgood bed: Clifton, Tennessee. 
Pterinea brisa, Hall. 
{Plate IV, Fig. 61.) 
Pterinea brisa was described by Hall in the Twentieth Regents 
Report the State Cabinet of Natural History of New York. The 
type was obtained at Bridgeport, Illinois. This is an entirely dif- 
ferent species from that identified as Pterinea brisa from the Wal- 
dron bed, Waldron, Indiana. Only a single specimen of Pterinea 
brisa was found in the Waldson bed at Newsom, Tennessee. This 
was a left valve. It has the following characteristics. 
Length of the umbonal ridge or general body of the shell, from 
the beak to the posterior end of the ridge, 20 mm. The poste- 
rior margin of the body makes an angle of about 30° with the 
hinge line; the anterior margin is nearly vertical. The anterior 
lobe begins about 9 mm. beneath the beak and extends forward 
about 5 mm. from the center of the beak. The extremity of the 
posterior lobe, along the hinge line, is about 18 mm. from the 
beak; the inner edge of the sinuous curve is about 16 mm. Radi- 
ating plications are numerous and sharply defined along the umbo- 
nal ridge or general body of the shell. At a distance of ii mm. 
from the beak, there are 13 to 15 striations in a width of 5 mm. 
anteriorly, becoming less frequent and less distinct on the posterior 
lobe, and reduced to mere crenulations or nearly obsolete on the 
anterior lobe. Concentric lines of growth rise as sharp narrow 
laminae, approximately equidistant on the same parts of the shell, 
about 12 in a length of 5 mm. at a distance of 10 mm. from the 
beak. These concentric striae become more distant toward the 
posterior lobe of the shell, and closely crowded together on the 
anterior lobe. While the radiating striae become stronger toward 
the anterior edge of the concentric striae or lamellae, they are not 
produced into fimbriae. 
