362 SYSTEMATIC PALEONTOLOGY 



eyes the papillae are much less conspicuous than upon the glabella and 

 the marginal border is perfectly smooth. Pygidium unornamented, 

 except by the grooves marking the segments, which do not extend entirely 

 to the border, thus leaving a plain, perfectly smooth, narrow marginal 

 border." Weller, 1903. 



Occurrence. CHAMBERSBURG LIMESTONE (Tetradium cellulosum bed) . 

 Several localities south of Chambersburg, Pennsylvania. This species 

 has hitherto been supposed to be restricted to the Trenton rocks of the 

 United States and Canada. 



Collection. U. S. National Museum. 



subclass EUCRUSTACEA 



Superorder BRANCHIOPODA 



Order NOTOSTRACA 



Genus RIBEIRIA Sharpe 



RlBEIRIA ? NUCULITIFORMIS Cleland 



Plate XXXI, Figs. 13, 14 



Ribeiria f nuculitiformis Cleland, 1900, Bull. Amer. Pal., vol. lii, p. 133 

 (261), pi. xvi, figs. 10-14. 



Description. Shell small, varying from 1.5 mm. by 3 mm. to 6 mm. 

 by 12 mm., compressed laterally, with the dorsal margin concave and the 

 sides convex. In casts, a deep notch about one-fourth the length of the 

 shell is shown just below the beak and extends obliquely towards the 

 middle of the ventral side. 



The shell of this interesting crustacean much resembles a species of the 

 pelecypod genus Nuculites, whence the specific name. 



Occurrence. BEEKMANTOWN LIMESTONE (Stonehenge member). 

 Hagerstown, Maryland. An extremely abundant fossil in the Tribes Hill 

 limestone at Fort Hunter, New York. 



Collection. U. S. National Museum. 



