ORISKANY SANDSTONE. 4Jl| 



Stropliodoiita iiiagniTentra. 



Plate XCII. Fio. 2 a 6 c, & 3 ; and Plate XCV. Fig. 9. 

 Strophodonla ma^ivetUra : Hall, R^ents' Report, 1857, p. 54; Paleeozoic Fossils, p. 14. 



Shell subsemicircular, varying to longitudinally suboval ; length usually 

 two-thirds the breadth, sometimes equal or greater. Ventral valve 

 convex in the central and umbonial regions, flattened towards the 

 extremities : beak slightly incurved ; cardinal border sloping from the 

 umbo ; hinge-line crenulated, equal to or greater than the greatest width 

 of the shell, sometimes extended into mucronate points beyond the 

 lateral margins. Area of ventral valve broad, slightly curved, distinctly 

 marked by vertical striae produced by the prolongations of the hinge t 

 foramen closed. 



Surface marked by regular, rounded, slightly elevated, radiating striae : 

 interior scarcely granulosa, having a plicated flabelliform muscular im- 

 pression, covering nearly two-thirds of its extent, and varying somewhat 

 in its form and proportions. The adductor muscles occupy a narrow 

 elongated oval space. 



The area sometimes shows a flat triangular space indicating the foramen, 

 but I have no evidence that it is ever free. In a single separate valve, 

 there is a strong central process underlying the area in the centre, with 

 a cavity on each side for the reception of the bifurcate cardinal process 

 of the other valve. 



Dorsal valve [ of this species ? ] deeply concave, radiatingly striated ; the 

 striae finer than those on the ventral valve. The interior of the valve 

 is marked "by well-defined muscular areas ; and outside of these, the 

 vascular and ovarian spaces occupy a large part of the shell, having 

 a well-defined semielliptical area of a width little greater than the 

 length, and somewhat contracted at the cardinal angles. The margin 

 outside of the vascular area is striato-punctate. 



This species has been determined from the strongly marked casts of tlie ventral 

 valve, its usual mode of occurrence in the Oriskauy sandstone. I have a single ven- 



