506 PALEONTOLOGY OF NEW YORK. 



SpHENOTUS (?) UNDATUS. 



PLATE LXXX, FIG. 6. 



In part SatiffiUrwlitea undatus. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 80, figs. 



.'), fi. 1883. 



Shell large, elongate-ovate, wider behind ; length more than twice the greatest 

 height ; basal margin nearly straight, gently curving to the posterior extrem- 

 ity and more abruptly curving anteriorly. Posterior margin oblique, gently 

 rounded or sub-truncate. Cardinal line straight, more than half the length 

 of the shell. Anterior end narrowly rounded. 



Valves depressed-convex in the basal and posterior portions, becoming con- 

 vex and scarcely gibbous in the umbonal region. 



Beaks sub-anterior, small, closely appressed, rising very little above the 

 hinge-line. Umbonal slope obtusely angular, extending to the post-inferior 

 margin. Post-cardinal slope wide, essentially flat, with a narrow, obscure 

 fold a little below the hinge-line. Cincture obsolete. 



Surface marked by fine concentric striae, which become fasciculate, pro- 

 ducing regular, strong, rounded folds or undulations, which are stronger on 

 the middle of the shell and become obsolete in passing the umbonal ridge. 

 Interior unknown. 



The specimen described has a length of 67 mm. and a height of 28 mm. 



This species differs from others referred to this genus in the strong concen- 

 tric undulations and in the absence or obsolescence of a cincture. It is placed 

 under this genus with some hesitation, since only two specimens have been 

 observed, and we have no knowledge of its interior characters. 



Formation and localities. In the sandstones of the Chemung group at Mans- 

 field, Pa., and Erwin, Steuben county, N. Y. 



