I 



LAMELLIBRANCHIATA. 407 



SPATHELLA, n. gen. 

 Spathella typica. 



PLATE LXVI, FIGS. 36-10. 



In part SanguinoHten ventricoims (White and Whitfikld), Halt,. Pal. N. Y., vol. v, pt. 1. Plates and 



Explanations : PI. G6, tigs. 36^2. 1883. 



Shell of medium or large size, from sub-cylindrical to elongate-ovate, wider 

 behind ; length from two and a half to less than twice the height ; basal 

 margin gently curved, sometimes nearly straight. Posterior extremity nar- 

 rowly or broadly rounded. Cardinal line straight, less than half the length 

 of the shell. Anterior end short, narrowly rounded below. 



Valves moderately convex posteriorly, gibbous in the middle and umbonal 

 region. 



Beaks anterior or sub-anterior, small, closely appressed, rising but little 

 above the hinge-line. Post-umbonal slope rounded or sometimes sub-angular, 

 extending to the post-inferior extremity. 



Surface marked by fine concentric striae, and at somewhat regular inter- 

 vals by sharp, lamellose striae. Interior unknown. 



Eight specimens measure respectively 46, 46, 45, 43, 38, 35, 32 and 32 

 mm. in length, and 24, 18, 20, 20, 16, 16, 15 and 14 mm. in height. 



This shell evidently belongs to the Lithophagi, but is not referable to any 

 known genus. The specimens are extremely variable in proportions, as shown 

 by the measurements, but are usually easily recognized by their sub-cylindrical 

 form and the distant lamellose elevated striae, which make a regular curve over 

 the posterior portion of the shell, turning forward to the cardinal line. This 

 character of surface somewhat resembles Macrodon, but the absence of radiat- 

 ing striae and the short cardinal line are distinguishing characters. 



Formation and localities. In the Chemung group, near Elmira and Ithaca ; in 

 Lindley township, Steuben county, N. Y. ; and in Sullivan, Tioga and Brad- 

 ford counties, Pa. 



