414 
PALAEONTOLOGY OF NEW-YORK. 
Stroplioctonta imignifica. 
Plate XCIII. Fig. 4; Plate XCIV. Fig. 2 a - d; and Plate XCY. Fig. 8. 
Strophodonta magnified : Hall, Regents’ Report, 1857, p. 54; Palaeozoic 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 
striae produced by the prolongations of the hinge crenulations; foramen 
sometimes a linear slit. 
Surface 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 
