MAItYLAXD C.EOLOGtCAI. SuRVEY 529 



Genus KLCEDENIA Jones and Holl 



IvLCEDENiA CENTRicoRXis Ulricli aiicl Bassler 



Plate XCVII, Figs. 1-4 



Kladenia centricornis Ulrich and Bassler, 1908, Proc. U. S. Nat. Mus., vol. 

 XXXV, pi. xxxviii, fig. 23. 



Description. — Valves very slightly oblique, elongate, subelliptical, the 

 relation of length to height being a little less than two to one ; hinge-line 

 long and straight, though shorter than length of the shell ; cardinal angles 

 subequal, generally rather obtuse ; ends nearly equal, cur\ing broadly into 

 the bowed ventral part of the outline. Surface of valves rather coarsely 

 reticulated or pitted and with the usual two furrows. The conical, some- 

 times spine-like form of the median node is the most peculiar feature of 

 the species. The contour of the remainder of the surface is about as usual 

 except that the ventral slope is uncommonly abrupt and the flattened 

 border a little wider than usual. 



Left valve, fig. 1, length 1.83 mm.; height 0.92 mm. ; left valve, fig. 2, 

 length 1.47 mm. ; height .76 mm. 



Both of the figured and only known specimens from Maryland are pro- 

 vided with a ventral pouch. This is situated rather far back and gives 

 the female valves a more oblique form than pertains to the male. Good 

 specimens of the latter from equivalent beds in the New York are con- 

 tained in the Ulrich collection at the U. S. National Museum. The un- 

 usual length of the valve, spine-like central node, and coarse pitting, are 

 features which will cause its easy identification and differentiation from 

 other species of the genus. 



Occurrence. — Helderberg Formatiox, Keyser Member. Cumber- 

 land. 



Collection. — U. S. National Museum. 



Ivlcedenia eimbkiata Ulrich and Bassler 

 Plate XCVII, Figs. 5-7 



Khrdenia fimbriata Ulrich and Bassler, 1908, Proc. U. S. Nat. Mus., vol. xxxv, 

 pi. xxxviii, fig. 22. 



Descnption. — This fine species will be recognized at once by its spinose 



margin. This spiney frill, together with the reticular surface ornament 



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