256 
PALAEONTOLOGY OF NEW-YORK. 
cipal ones towards the margin, in each of which are four or five striae ; a slight depression 
along the centre of the ventral valve. 
The specimens figured are casts of the two valves, the one showing the hinge-line to be 
much more extended than the other. The striae are evidently in distinct fascicles like O. Jissi- 
costa of the lower silurian strata, but it is a very different shell. 
In a fragment of shale from Lockport, the surface of this shell is preserved, showing the 
concentric striae crossing the diverging ones. 
Fig. 8 a. A cast of the"/ventral valve, showing an extended hinge-line. 
Fig. 8 b. A cast of the dorsal valve. 
Position and locality. In the shale’at Rochester and Lockport. 
618. 24. LEPTaENA TRANSVERSALIS. 
Pl. LI1I. Fig. 5 a - l. 
Anomites transversalis. Wahlenberg, Act. Soc. Upsaliensis, 1821, Vol. iii, p. 64, n. 4. 
Leptcena transversalis. Dalman, Vet. Acad. Handl. 1828, pag. 109, pi. 1, fig. 4. 
— — Hisinger, Pet. Suecica, 1887, pag. 69, pi. 20, fig. 5. 
— — Murchison, Silurian System, 1889, pag. 629, pi. 13, f. 2. 
Strophomena transversalis. Hall, Geol. Report, 1843, p. 105, and fig. 4, p. 104. 
Semicircular ; dorsal valve very convex ; ventral valve extremely concave, conforming to 
the dorsal valve ; hinge-line inflected, equal to or longer than the width of the shell below. 
Surface marked by distant elevated striae or ribs, with the interstices more finely striated : a 
few strong concentric lines of growth sometimes occur near the base. 
This shell resemples L. sericea in the characters of the surface ; but it is usually less extended 
laterally, proportionally longer, and much more convex. The cast of the shell likewise presents 
a very different character, being striate or puncto-striate instead of punctate only. It is one 
of the most common shells of the shale, but it is nevertheless difficult to obtain good spe¬ 
cimens. 
Fig. 5 a, b, c. Dorsal and ventral views of two small individuals, where the hinge-line is much 
extended into acute points. 
Fig. 5 d. A larger specimen, where the hinge-line is slightly extended on one side, while the 
other is less extended. 
Fig. 5 e, f. Dorsal and ventral views of a large individual, having the hinge-line slightly ex¬ 
tended. Individuals so large as this one are rarely found. 
Fig. 5 g. Cardinal view, showing the extreme convexity of the dorsal valve, and the inflection 
of the cardinal margin. 
Fig. 5 h. An enlargement of the surface, showing the coarser striae with intermediate finer ones. 
Fig. 5 i. The interior, showing a striato-punctate character, with reticulations like the lines of 
bloodvessels. 
Fig. 5 k. The interior of the ventral valve, showing the strong parallel laminae, and prominent 
points on either side for the muscular attachment. 
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