256 



PALJEONTOLOGT OF NEW-YORE. 



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 arc 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 6. A cast of the dorsal valve. 



Position and locality. In the shale^at Rochester and Lockport. 



618. 24. LEPTiENA TRANSVERSALIS. 



Pl. LIII. Tig. 5 a- I. 



jfnomites transversalis. Wahlekbbrg, Act. Soc. Upsaliensii, 1821, Vol. iii, p. 64, n. 4. 

 Ltptana transversalis. Dalman, Vet. Acad. Handl. 1828, pa|». 109, pl. 1, fig. 4. 



— — HisiNGER, Pet. Suecica, 1837, pag. 69, pl. 20, fig. 5. 



— — Mcp.CHisoN, Silurian System, 1839, pag. 629, pl. 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 strife with intermediate finer ones. 



Fig. 6 i. The interior, showing a striato-punctate character, with reticulations like the lines of 

 bloodvessels. 



Fig. 6 k. The interior of the ventral valve, showing the strong parallel laminre, and prominent 

 points on either side for the muscular atiachment. 



