528 Syste:matic Paleontology 



greatest amount of curvature in the posterior portion; dorsal margin 

 straight. Inner ridge thick, regularly U-shaped, with the ends slightly 

 bulbous and reaching the dorsal margin; outer ridge imperfectly de- 

 veloped and coalescing with the inner ridge along the ventral side ; dorsal 

 ends of outer ridge free, but reaching little more than halfway across the 

 valve ; anterior arm of outer ridge narrow and drawn out ; posterior end 

 thick and bluntly rounded ; edge of valves marked by a somewhat obscure 

 marginal rim. 



Length 1.40 mm. ; height .94 mm. 



The union of the inner and marginal ridges along the ventral portion, 

 suggesting the specific name, is the distinguishing and characteristic 

 feature of this species. The associated B. americana is of similar shape 

 and size, but the surface configuration of each is sufficiently distinct to 

 admit of no confusion in identification. A similar union of the inner and 

 outer ridges along the ventral side is unknown to us in any other species 

 of the genus, so that in this respect B. jugalis seems to be unique. 



Occxi,rrence. — Oriskany Formation, Sheiver Member. 21st Bridge. 



Collection. — U. S. National Museum. 



BoLLiA UNGULA Jones 



Plate XCVI, Figs. 20-22 



Bollia ungula (Claypole MS) Jones, 1889, Amer. GeoL, vol. iv, p. 338. 

 Bollia ungula Ulrich, 1891, Jour. Cincinnati Soc. Nat. Hist., vol. xiii, p. 188, 

 pi. xiv, figs. 6a, 6&. 



Description.— The geologic range of this widespread Bollia has been 

 considerably extended by the discovery of specimens in the siliceous dark 

 shales of Lower Oriskany age at 21st Bridge. Hitherto the species has 

 been known only from strata of Middle Devonian age in the various parts 

 of the eastern half of the United States. With the exception of a slight 

 variation in the marginal rim, these Oriskany specimens differ but little 

 from examples in the type horizon. 



Length .77 mm. ; height .47 mm. 



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



Collection. — U. S. National Museum. 



