 •• PALiEONTOLOGY OF NEW-YORK. 



Orihis nigosa : D'Archiac et Db Vbbneuil, Trans. Geol. Society London, 1842, 2d series, Vol.vi, 



part 2, p. 396. 

 Strophomena drprtua : Vanuxkm, Geol. Report Third District New-York, 1842, i>a. 79, f. 5. 

 S. undulata : Id. lb., pa;^139, f. 3. 



S. deprtssa : Ball, Geol. Report Fourth District New-York, 1843, pa. 77, f. 5; and pa. 104, f. 2. 

 Ortkis rxigosa : F. C. R(EHEr, Rhein. Ucbergangsgcbirge, 1844, pp. 85 & 90. 

 Leplttna depreasa : Dk Vernkuil, Geol. Russ. and the Ural, 1845, Vol. ii, pa. 234, pi. 15, f. 7. 

 — — Hall, PalBBontology of New-York, 1847, Vol.ii, p. 257. 



Strophomena rhomboidalu : Datibson, Intr. Nat. Ilist. Brachiopoda. 



Shell varying from semioval to semicircular. Hinge line equalling or 

 greater than the width of the shell below : cardinal extremities often 

 much extended. Dorsal valve flat or slightly concave in the upper part, 

 and abruptly curving or inflated towards the front : beak prominent, 

 perforate at its apex, and filling a deep sinus in the opposite valve. 

 "Ventral valve slightly convex or nearly flat in its upper part, and 

 sometimes even concave ; convex upon the umbo, often perforate near 

 the beak ; abruptly deflected or geniculate towards the front : cardi- 

 nal area narrow, linear, partially occupying both valves. Foramen of 

 the ventral valve a broad, shallow sinus, which is filled by the promi- 

 nent cardinal process of the opposite valve, the latter being perforate 

 or deeply grooved for the passage of a pedicle. 

 Surface marked by regular, rounded, radiating striae, which increase by 

 bifurcation and interstitial addition : the upper part of the valves 

 marked by strong concentric wrinkles which do not extend below the 

 abrupt bending of the valves. 



The interior of the shell is striato-punctate, or sometimes simply 

 punctate. The muscular areas of the ventral valve are strong, more or 

 less deeply bilobed, and limited by the extension of the dental lamellae. 

 The interior of the dorsal valve is strongly marked by the muscular 

 impressions ; the dental process perforate near its outer surface, or 

 deeply grooved ; and there is often a deep cavity below this, extending 

 towards the beak. 



This shell exhibits much variety of form, being sometimes nearly flat or but 

 slightly curved near the margin; and the corrugations are variable in number and 

 strength. In very old shells they are often not as prominent as in younger ones, or 

 those of medium size. The area, as usually exposed, is subject to much variation, 



