260 



PALJEONTOLOQY OF NEW-YOKK. 



Fig. 8 c. The striee enlarged. 



Fig. 9 a. Cast of the ventral valve, apparently identical with the preceding, showing the mus- 

 cular impression and the remains of the dental laminiB. 



Fig. 9 h. The interior of the valve of another specimen, showing the dental lamins of the same 

 form as in the [jreccding figure. 



Fig. 10 a. A large individual having sharp prominent strice which are dichotomous, and cios6i;J 

 by finer stria;, which remain in the depressions only. 



Fig. 10 c. Several of the strioe enlarged, showing the concentric striie. 



Fig. 10 b. Cardinal view of another similar specimen, showing the narrow extended area and 

 foramen. 



This shell has the character of an Ortiiis in many respects. The valves are almost equally 

 convex, one being usually quite flat, e.Kcept near the beak ; while the other is plano-convex at 

 the beak, and slightly convex below. I have united the forms given above, believing them to 

 belong to the same variable species, the ditlVrent appearances being often caused by partial 

 exfoliation of the shell. 



Position and locality. This species occurs in the shale at Lockport, the most perfect speci- 

 mens being found adhering to the thin calcareous layers. In other localities this shell is less 

 conspicuous, though occurring at Rochester and Wolcott, and probably at intermediate places. 



621. 4. SPIRIFER BILOBUS (Linne). 



PL. LIV. Fig. To-*. 

 Jlnoniia. Linke, Syst. p. 1154. 



Terebratula sinuata. Sowebby in Linn. Transactions, Vol. xii, p. 616, t. 23, f. 5 and 6. 

 Terebratula cardiospcrmiformis. Hisinger, Acta. Soc. Holmiensis, Vol. iv, p. 18, pi. 7, f. 6. 

 DeltkyrisJ — D.ilman, Vet Acad. Handl. 1827, pag. 124, tab. iii, fig. 7. 



— — Hisinger, Petrcf. Suecica, 1837, p. 74, t. 21, f. 9. 

 Spirifer cardiospermiformis. Vow Buch, Sur les Spirifer et Orthis, T. 1, f. 7. 



— sinuatus. Sowerby in Murchison's Sil. System, 1839, pag. 630, pi. 13, fig. 10. 

 Dclthyris sinuatus. Hall, Geol. Rep. 4th Dist. N. York, 1843, pag. 105, fig. 8. 



Shell bilobate, obcordate, sinuate in front ; extremities of the cardinal line auriculate ; dorsal 

 valve very convex, arcuate ; ventral valve flat or slightly concave (rarely a little convex) ; area 

 comparatively large, triangular, with a distinct triangular foramen ; surface striated ; striae 

 dichotomous or in fascicles, radiating from the apex to each lobe of the shell ; concentrically 

 marked by fine stria;, which are deeply arched or sinuate in the sinus of each valve ; hinge-line 

 of ventral valve marked on its inner margin by three simple teeth. 



This peculiar little species is readily distinguished from any other known, except a closely 

 allied form in the Delthyris shaly limestone. Our species is evidently identical with the 

 European one, as proved by a comparison with Swedish specimens, and the figures in the 

 Silurian System cited above. The species of the shaly limestone of New- York attains a larger 



