CLINTON aaoup. 



59 



146. 9. LEPT^NA SERICEA. 



Pl. XXr. Fig. 1 a, 6, c, d, e. 

 For synonymy and references, see Pal. N. York, Vol. i, p. 110, 

 Strophomena elegantula. Hall, Rep. 4th Geol. Dist. N. York, 1843, pa^. 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. 



t-, M. DE Verneuii. 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, b}'" 

 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. 



Fi"'. 1 J. 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 strice. 

 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. LEPT^NA CORRUGATA. 



Pi. XXI. Fig. 2 a, b, c, d, e, f. 

 Strophomena cor rugat a. Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, pag. 256, pi. 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 striee, 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. 



