24 On Lingulasma^ Etc. — ULrich. 
Shell broadly oval to sub-pentagonal, wider than long, with 
the beak of the dorsal valve, and generally the anterior and 
posterior angles, slightly produced. Dorsal valve, when found 
in a shale matrix, only moderately convex, but specimens oc- 
curring in limestone have suffered less through compression, 
and are strongly convex, particularly in the region a little pos- 
terior to the middle. Umbo tumid with the cardinal slopes 
abrupt and occasionally slightly concave. Front margin 
nearly straight or gently convex, rounding more or less 
abruptly into the lateral borders. Beak acutely rounded, in- 
curved to the plain of the posterior margin. Surface with ob- 
scure concentric lines and radiating series of punctures. The 
latter are usually absent, over the concentric region of the 
valve, are larger than in T. u77ibo7iata, increase in size outward, 
and near the front margins of large specimens form a network 
similar to that of T. ottawaensis and crassipuncta^ only the 
meshes are not as large and the radial lines wider than in 
those species. 
Ventral valve, so far as observed perfectly flat, save at the 
small impressed area at the bottom and posterior end of which 
is situated the small foramen notch. Surface with rather ob- 
scure concentric lines and radial series of punctures near the 
outer borders. 
This species has generally been considered identical Avith 
T. punctostriata, described by Hall from hydraulic limestone 
of Trenton age (probably equivalent to the " Modiolopsis 
bed " of central Kentucky, at Clifton Terrace. Against this 
view I have only this to say, that if Hall's original figures are 
correct, and no one so far as is known to me claims that they 
are not, then the Cincinnati specimens clearly belong to a dis- 
tinct species. It must be confessed, however, that the surface 
ornamentation seems to be very similar in the two forms and 
that they are in all probability closel}^ related. Still, there 
are enough points in which they disagree to make a separa- 
tion desirable and practicable. There is always a slight differ- 
ence in the outline, and the umbonal region and the beak of 
the dorsal valve are more pronounced. Figs. 9 and 9 b of this 
paper illustrate extremes of variation in outline, while Hall 
and Whitfield's fig. 8, pi. i, vol. ii, Ohio Paleontologi/, repre- 
sents an average specimen. In comparing the ventral valve a 
more decided diff"erence is noticed, the foramen notch in the 
