414 PALJ:0NT0L0GY of NEW-YORK. 



Stropiiodoiita iiia«:iiifica. 



Plate XCHI. Fia. 4 ; Plate XCIV. Fio. 2a-</; and Plate XCV. Fio. 8. 

 Stropkodonta magn!fita : IIall, Regents' Report, 1857, p. 54; Palnozoic Fossils, 1857, p. 14. 



Shell very large, transversely suboval longitudinally, somewhat semi- 

 elliptical, more or less rounded at the extremities of the hinge ; length 

 and breadth about as four to five, or as seven to eight. Ventral valve 

 depressed-convex in the middle and umbonial regions, flattened near 

 the lateral extremities : cardinal margin sloping gently from the beak. 

 Dorsal valve slightly concave, sometimes flat in the middle : hinge-line 

 crenulated, usually a little less than the width of the shell, sometimes 

 greater. Area narrow, distinctly and regularly marked with transverse 

 strias produced by the prolongations of the hinge crenulations; foramen 

 sometimes a linear slit. 



SoBPACB marked by somewhat faint radiating striae, which bifurcate re- 

 gularly about two or three times at uniform distances from the beak. 



The interior of the ventral valve is marked by a large flabelliform 

 muscular impression, the sides of which are straight and bordered by an 

 elevated ridge or crest, while the- divisions are sharply defined : the 

 whole gradually becomes obsolete on the anterior or basal margin. The 

 thickened process beneath the area in the centre is usually perforated by 

 a round or oval foramen, leaving a narrow slit in place of the triangular 

 opening. 



The interior of the dorsal valve of this species, as shown by the im- 

 pressions in sandstone, and in a single imperfect valve, shows a broad 

 vascular area, which is defined by a low flattened ridge, or sometimes a 

 more distinctly marked border, on the outside of which the shell is more 

 abruptly curved. The impressions of the cardinal muscles are narrow 

 subreniform, and in proportion are wider than those of S. vascularia, 

 while they are narrower than those of S. magniventra. In well-preserved 

 specimens there is a defined subreniform vascular area below the cardinal 

 muscular impressions on each side, and a similarly marked space, a little 



