526 Systematic Paleontology 



B. hicollina, noted in the bibliography above, but from each it can be 

 separated by slight although important differences. 



Length of left valve 1.24 mm.; height of same .9 mm. 



The outline of the valves in B. uniflexa and B. americana is practically 

 identical, but the former has a reticulate surface and a slightly developed 

 marginal ridge. In B. bicollina the valves are more equal ended than in 

 the American species, while further differences may be noted, especially 

 in the marginal ridges of the tv^o species. There are sharp protuberances 

 or crests in B. bicollina closely paralleling the edge of the valve and con- 

 tinuing to the dorsal border. The marginal ridge in B. americana, how- 

 ever, is more rounded and like the inner ridge, thickens slightly into 

 terminal knobs before the hinge is reached. 



Bollia americana, B. uniflexa, and B. bicollina are three well-marked 

 members of the typical section of Bollia, namely that division of the 

 genus in which the outer ridge is not strongly developed while the inner 

 ridge has bulbous ends connected by a narrow bent portion. No American 

 species is known closely resembling it to make comparisons necessary. 



Occurrence. — Oriskany Formation, Shriver Member. 21st Bridge, 

 Cash Valley. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Bollia curta n. sp. 

 riate XCVI, Figs. IG, 17 



Description. — Carapace subcircular except along the short, straight 

 hinge, with ends strongly and almost equally curved ; dorsal angle obtuse, 

 hinge straight and rather short ; outer ridge thin, inconspicuous, parallel- 

 ing and closely following the margin and reaching the dorsal edge with 

 its ventral part showing a neat row of papilla? ; inner ridge thick, equally 

 developed throughout, occupying the greater portion of the valve, but not 

 extending to the hinge margin; the included sulcus narrow; surface of 

 valves papillose. 



Length of valve .76 mm. ; width .GO mm. 



