1 1 i:i.i)i:i;i!i:i;(; Kokmaiiox in Makyi.and 13 



SciiucirEijTELLA sixuATA (Hall ;U!(1 Clarke) 

 Plato LXI, Figs. :\, 4 



Orthothctcs deformis var. sinuatiis Hall and Clarke, 1892, Nat. Hist. N. Y., 

 Pal.. VQl. viii, pt. i, pi. 20, figs. 8 and 9. 



Description. — Two views of a specimen arc flgurcHl but not dci-crihed 

 by Hall and Clarke, wbieli sliow the distortion of the beak and the median 

 sinus on the brachial vahe. Hall says " Furtlier examination will prob- 

 ably prove this form to be a distinct species." This fossil was collected at 

 Cumberland, Maryland, by Hall and is cited from the rocks of the Lower 

 Helderberg. The individual at hand consists only of the brachial valve. 



Brachial valve transversely subelliptical in outline, wider than long, 

 extremely convex, gibbous, greatest convexity about 3 mm., anterior to the 

 bealv, sloping somewhat abruptly to the lateral margins, there becoming 

 plane to concave. Hinge-line straight and less than the greatest width 

 of the shell. Lateral and front margins rounded ; beak strongly incurved. 

 A somewhat shallow sinus extends from the beak to the front, gradually 

 becoming broader from the beak anteriorly. Surface marked by well- 

 defined simple tubular ribs which increase by interstitial addition and 

 implantation. 



Dimensions : Length 17 mm. ; width 22 mm. 



This species differs from Sckuchertella deformis in (1) having the 

 dorsal valve extremely convex, (2) being transversely subelliptical in out- 

 line while 8. deformis is suborbicular lenticular, (3) having a well-defined 

 sinus in the dorsal valve. 



Occurrence. — Helderberg Formation, Keyser Member. Devil's 

 Backbone. Beneath the Gypidida coeymanensis var. prognosiica zone. 



Collections. — U. S. National Museum, American Museum of Natural 

 History. 



ScHUCIIERTELLA MARYLANDICA U. Sp. 



Plate LXI, Figs. 5-9 



Description. — Shell plano-convex, subelliptical in outline. length 

 greater than the width. Lateral and anterior margins rounded. Hinge- 

 line straight, about two-thirds the greatest width of the shell. Cardinal 

 area high, triangular in outline. Pedicle valve convex, ventricose along 



