SCHUCHERTELLA 57 



the surface slightly compressed towards the cardinal extremities ; median 

 portion of the valve a little flattened anterior to the middle but not de- 

 pressed in a mesial sinus ; beak apparently obtusely angular, but slightly 

 protuberant beyond the cardinal margin; cardinal area rather low, ap- 

 parently flat and lying nearly at a right angle to the plane of the valve, 

 the lateral margins sharply denned and angular, sloping in nearly 

 straight or slightly concave lines from the beak to the cardinal extrem- 

 ities; the delthyrium broadly triangular, its apical portion closed by a 

 convex deltidium. Internally the dental plates are apparently obsolete; 

 the flabellate muscular scars are of medium size, but are illdefined and 

 only slightly impressed. 



Brachial valve about equally convex with the pedicle, but with the 

 greatest convexity situated farther towards the front, apparently anterior 

 to the middle in the type specimen, the surface compressed towards the 

 cardinal extremities, the umbonal region flattened; the mesial portion of 

 the valve depressed in a shallow and rather broad, ill-defined mesial sinus ; 

 the beak inconspicuous. Internal characters not observed, although the 

 posterior extremity of a rather broad cardinal process is exhibited 

 in the type specimen. 



Surface of both valves marked by fine, subangular, radiating costse 

 which are slightly irregular in size, separated by rather deep intercostal 

 furrows, about three occupying the space of 1 mm. Crossing the costae 

 are fine, concentric markings which seem to be more conspicuous towards 

 the cardinal extremities, in which portion of the shell the radiating 

 costae are minutely serrate by reason of the crossing of the concentric 

 lines. A few rather faint concentric lines of growth are present upon 

 the body of the shell, but in old examples they become very strong near 

 the margins of the valves. 



Remarks. This species resembles S. lens from the Louisiana limestone, 

 but it attains a much larger size, is proportionally broader, and is marked 

 by somewhat finer radiating costaa. The smaller, immature examples of 

 about the average size of 8. lens may be distinguished from that species 

 by their form and costae. 



Horizon. Fern Glen formation. 



SCHUCHERTELLA COSTATULA (Hall and Clarke) 



Plate II, Figs. 19-22 

 1892. Derlya (?) costatula Hall and Clarke, Pal. N. Y., vol. 8, pt, 1, 



p. 346, pi. 11B, figs. 16-17. 



1897. Derbya ( ? ) costatula. Hall, 14th Ann. Rep. N. Y. State Geol., p. 346, 

 pi. 5, fig. 9. 



Description. Shell small, broader than long, the hinge-line as long or 

 nearly as long as the greatest width of the shell, the cardinal extremities 

 angular. The dimensions of the holotype are : length of pedicle valve 



