geological position, as well as in the succeeding strata. (See the same in fossils of Lower Hel- 
derberg rocks.) ( State Collection.) 
619. 25. LEPT.ZENA STRIATA. 
Pl. LIII. Fig. 7. 
Strophomena striata. Hall, Geol. Rep. 4th District, 1843, pag. 104, fig. 3. 
Compare L. corrugata, page 59 of this volume. 
Shell semielliptical; hinge-line equal, or a little longer than the width of the shell; dorsal 
valve slightly convex, ventral valve flat. Surface finely striated ; striae crossed by concentric 
striae, which are not always conspicuous. 
I have been unable to obtain specimens of this shell in a condition to examine the interior, 
and I have some doubts regarding its specific distinction. The striae are apparently more round 
than in L. subplana ; but in a few specimens I have detected some slight plications near the 
hinge-line, which, with the round concentric striae, give it the appearance of L. corrugata of 
the Clinton group. 
All the specimens examined are extremely compressed, and closely adhering to the shaly 
laminae. 
620. 26. LEPT^ENA SUBPLANA. 
Pl. LIII. Figs. 8 - 10. 
Strophomena subplana. Conrad, 1842, Jour. Acad. Nat. Science, Yol. viii, p. 258. 
— — Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 104, fig. 1. 
Shell resupinate, semielliptical, length and width often nearly equal ; hinge-line extending 
beyond the width of the shell. Surface marked by prominent sharp striae, which frequently 
bifurcate before reaching the margin ; radiating striae crossed by strong concentric striae. Car¬ 
dinal area extending to the extremities of the hinge-line, narrow, partially formed by both 
valves. 
In a few well preserved specimens the sharp dichotomous striae are well preserved, having 
the character described by Mr. Conrad ; while in other specimens, apparently of the same 
species, the radiating striae are less prominent, and less conspicuously crossed by concentric 
striae. The specimen fig. 10 a has precisely the characters of the one described by Mr. Conrad, 
as I have ascertained by comparison ; but those of figs. 8 and 9 have more rounded striae, and 
are somewhat proportionally shorter. I have not, however, been able to find decisive characters 
for the separation of species. 
Fig. 8 a. The interior of the convex valve of a young individual, where the width is greater 
than the length, the extremities of the hinge-line being extended beyond the width 
of the shell below. 
Fig. 8 b. A specimen from which the shell is partially removed, showing, near the beak, the form 
of the muscular impression, etc. 
