Silurian Fossils 
69 
faint concentric striations are visible under a lens. This species 
is distinctly smaller than Rhombopteria ulrichi. The largest speci- 
mens do not exceed 22 mm. in length when measured along the 
umbonal ridge. Considering the small size of the shell, the longi- 
tudinal striations of the right valve are very conspicuous. 
An examination of the cast of the type of Rhombopteria revoluta 
does not reveal specific differences between this type and the New- 
som specimens, but the type is an imperfect exterior cast of the 
right valve only. In the Newsom specimens the shallow depres- 
sion limiting the anterior lobe from the body of the shell appears 
more distinct, the resulting concavity of outline between this lobe 
and the body is more readily discernible, and the radiating striae 
meet the hinge line of the posterior wing at a greater angle. If 
these features should prove to be fairly constant differences, when 
more is known of the Bridgeport species, the Newsom specimens 
might be called Rhombopteria divaricata. 
Waldron bed: Newsom, Tennessee. 
Conchidium legoensis. 
{Plate II, Figs. 56 A, B.) 
Closely related to C. crassiplicay but the shell is smaller, the 
plications are angular rather than rounded anteriorly, and there 
are ii to 14 radiating plications, none of them bifurcating ante- 
riorly. Length 29 to 31 mm., width 20 to 24 mm., thickness 16 
to 17 mm. Brachial valve depressed along its entire length. Beak 
of the pedicel valve erect, apex of brachial valve concealed, sides 
of shell distinctly flattened posterior to the middle. 
Brownsport bed : northeast of Lego on Short creek, 300 yards 
southeast of W. E. Ashley and P. Denman, along hillside south 
of the valley, Tennessee. 
Conchidium lindenensis. 
{Plate II, Figs. 35 A, B.) 
In form of shell and closeness of radiating plications most nearly 
related to C. colletti, but the shell is smaller, there are only 19 
radiating plications in the entire width of the shell at a distance 
of 30 mm. from the beak where C. colletti would show 34 plica- 
tions; moreover, the shell is narrower, and does not possess the 
frequent lines of growth. Length of largest specimen, 50 mm. 
