GASTROPODA. 827 
Helcionopsis striata.] 
in his genus T’ryblidium with the specific name radiatum. It is very closely related 
to our H. striata. Unfortunately we know very little of the muscular scars of these 
species, so that it is difficult to decide whether their affinities are nearer Tryblidium 
or Archinacella. What is known of them agrees better, as does also the form of the 
shells, with species of the former genus, while they are distinguished from both by 
the distinct radial sculpture of their surfaces. The marginal position of the apex 
separates them from Scenella, Billings. Stenotheca, Salter, includes laterally 
compressed and much higher shells. 
The generic name is from the external resemblance which the species bear to 
the recent species of the genus Helcion, Montfort. 
Hetcronopsis striata, n. sp. (Ulrich.) 
PLATE LXI, FIGS, 29 and 30. 
Shell rather strongly convex, acuminate-ovate in outline, broadly and regularly 
rounded behind, pointed in front where the apex projects slightly beyond the margin 
of the aperture; apex incurved. Surface marked by distinct, rounded, radiating 
lines, which in the outer half maintain an approximately equal size through 
bifurcation; about ten lines in 5 mm.; whole surface with very fine concentric lines; 
at intervals of 1 to 3 mm. irregular wrinkles marking stages of growth. Length 
24.5 mm.; width about 19 mm.; greatest hight 9 mm.; hight of apex about 4.5 mm. 
This species is quite distinct from all American patelliform shells, but is closely 
related to the Upper Silurian H. radiata Lindstrém sp.* As figured that species is 
a little more convex, the anterior outline blunter and the apex more incurved. 
Formation and locality—Rare in the upper beds of the Cincinnati formation, Marion county, 
Kentucky. Also, though of smaller size, in the Loraine group at Cincinnati, Ohio. 
Collection.—E. O. Ulrich 
HELcIONOpPSIS SUBCARINATA, 7. Sp. 
PLATE LXI, FIG. 28. 
Shell small, subovate in outline, the anterior and posterior margins subequal 
and sharply rounded in the middle. In the cast the apex is depressed, small and 
not quite marginal; an obtuse carination extends across the length of the shell. 
Surface of cast showing remains of very fine radiating lines, scarcely visible without 
a magnifier, and a few obscure lines of growth. Length 10 mm.; width 8 mm.; 
greatest hight 3.5 mm.; hight of apex 1.5 mm. 
We have only two specimens of this interesting species. Both are casts and 
show impressions of the rostral muscles. One exhibits besides a series of muscular 
scars similar to those of Tryblidium. The lines converging from them towards the 
* Silurian Gastropoda and Pteropoda of Gotland, p. 58; 1886. 
