196 
PALAEONTOLOGY OF NEW-YORK. 
Ortkis rugosa : D’Arciiiac et De Verneuil, Trans. Geol. Society London, 1842, 2d series, Vol.vi, 
part 2, p. 396. 
Strophomeiia depressa : Vanuxem, Geol. Report Third District New-York, 1842, pa. 79, f. 5. 
S. undulata : Id. Ib., pa. 139, f. 3. 
S. depressa : Hall, Geol. Report Fourth District New-York, 1843, pa. 77, f. 5; and pa. 104, f. 2. 
Ortkis rugosa : F. C. R(emer, Rhein. Uehergangsgehirge, 1844, pp. 85 & 90. 
Lepteena depressa : De Verneuil, Geol. Russ, and the Ural, 1845, Vol. ii, pa. 234, pi. 15, f. 7. 
— —• Hall, Palaeontology of New-York, 1847, Vol.ii, p.257. 
Strophomena rhoniboidalis : Davidson, Intr. Nat. Hist. 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 strke, 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 lamellse. 
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, 
