I2 4 



NEW YORK STATE MUSEUM 



Kayser's ' figures. There is no stable specific difference herein. All are 

 expressions, with slight divergence and local persistence, of the L . e x p 1 a- 

 n a t a type. 



Orthothetes (Schuchertella) cf. deformis Hall 



Plate 31, figures 1-4 



&Orthis deformis Hall. Palaeontology of New York. 1859. 3: 174, pi. 15, fig. 3 

 Orthothetes deformis Hall & Clarke. /#/</. 8: 255 



A very much distorted species of this genus with short hinge line, 

 broad, much elevated cardinal area, similar in aspect to, though of smaller 

 size than the species cited. This shell is known from a half dozen ventral 

 valves all highly rugose, especially on the earlier parts of the shell, and 

 some showing a large cicatrix of attachment which must have continued to 

 comparatively late growth. Even the strongly developed deltidium is 

 affected by the irregular growth. 



The surface of these valves is sharply and closely striated. 



Locality. Edmunds Hill. 



Hipparionyx minor Clarke 



Plate 31, figures 16-32 



Hipparionyx minor Clarke. N. Y. State Mus. Bui. 107. 1907. p.278 



The recognized distinction between the genera Hipparionyx and Ortho- 

 thetes or Schuchertella lies chiefly in the orthoid form of the former and its 

 very short hinge line. In respect to this character the specimens before us 

 are pronounced. The ventral valves, small in comparison with those of 

 H. proximus, have a short and low cardinal area, but in the dorsal valves 

 the hinge line is apparently longer than correspondence with the opposite 

 valve requires and these valves convey the impression of a straight and 

 tolerably long line extending more than one half the width of the shell. On 

 examination of the inner surface of this valve it is seen that this area is 

 really short and confined to the apical part of the valve while the extended 

 extremities are a thin expansion of the lateral parts of the valve which 

 make a rather sharp turn at the cardinal angles. There is other divergence 

 in the shell away from the type of Hipparionyx and toward that of Ortho- 

 thetes as represented by such shells as Streptorhynchus umbra- 

 c u 1 u m Schlotheim and its variant expressions. 



In further detail, the ventral valve is subcircular or transverse with 

 strongly defined and thickened adductor and divaricator scars. These are 

 not, however, as large as in H. proximus. The beak is convex and 

 slightly elevated but the rest of the valve is depressed or flat with a ten- 

 dency to turn up about the margin and with indications of a broad and low 



1 Fauna d. Hauptquarzits, pi. 21, 22, fig. i. 



