CLINTON GROUP. 
59 
146. 9. LEPTiENA SERICEA. 
Pl. xxr. Fig. 1 a, b, c, d, e. 
For synonymy and references, see Pal. N. York, Yol. i, p. 110. 
Strophomena elegantula. Hall, Rep. 4th Geol. Dist. N. York, 1843, pag. 73 ; fig. 1, p. 72. 
Semicircular or semioval; hinge-line extending beyond the length of the shell, into acute 
points; surface marked by strong elevated striae, and finer ones between; dorsal valve very 
convex. 
, . M. de Verneuil has suggested that the S. elegantula cited, is identical with the L. sericea of 
the lower strata; and on a careful comparison, I am unable to find constant characters, by 
which to distinguish the one from the other. The specimens in the Trenton limestone and 
Hudson-river group rarely show the great difference in the size of the striae, which are so con • 
spicuous in the Clinton specimens. The dorsal valve in the latter specimens is always very con¬ 
vex, and much more so than in specimens from the lower rocks. The Clinton specimens often 
show a depression, commencing at the beak of the convex valve, expanding towards the centre 
of the valve, and becoming obsolete below. This feature is not conspicuous in specimens from 
a lower position. Still I am unable to show constant and reliable characters to distinguish this 
as a species. 
Fig. 1 a. A large individual, preserving the shell nearly entire. 
Fig. 1 b. A specimen preserving a portion of the shell, and showing in the cast the puncta which 
are so characteristic in this species. 
Fig. 1 c. A cast of the same, showing the strong puncta produced by the small spines of the 
interior of the shell. 
Fig. 1 d. A portion of the shell enlarged, showing the larger and smaller stri®. 
Fig. 1 e. A similar portion of the cast, showing the puncta. 
Position and locality. This species is found in the green shale at Rochester ; also at Sodus 
in Wayne county, associated with Graptolithus clintonensis, and with Atrypa reticularis. 
(State Collection.) 
443. 18. LEPTiENA CORRUGATA. 
Pl. XXI. Fig. 2 a, b, c, d, e, f. 
Strophomena corrugata. Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, pag. 256, pl. 14, fig. 8. 
— — Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 73, fig. 2, p. 72. 
Semioval, nearly flat; hinge-line extending into small acute ears; surface marked by fine 
prominent striae, which alternate with finer ones ; striae usually unequal, but often equal in size 
and regularly bifurcating, crossed by fine concentric lines ; the hinge-margin marked by oblique 
folds, which are sometimes obsolete : cast striated, except on each side of the beak and below, 
where it is punctate. 
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