Maryland Geological Survey 527 



The subcircular outline^ unusual development of the inner ridge, and 

 the insignificant outer rim, cause this species of Bollia to be easily 

 recognized. 



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



Collection. — U. S. National Museum. 



Bollia irregularis n. sp. . 

 Plate XCVI, Fig. 18 



Description. — Carapace elongate, subelliptical, the length about one and 

 two-thirds times the height, hinge-line approximately straight, anterior 

 and posterior ends about equally rounded, ventral margin gently curved 

 with a slight backward swing of the anterior outline; edges of valves 

 thick, forming the marginal ridge which extends practically to the dorsal 

 line at each end; marginal ridge along posterior end thinner than the 

 corresponding anterior portion and slightly constricted in the lower third ; 

 inner ridge irregularly U-shaped with the posterior arm refiexed and 

 slightly bulbous ; spaces between ridges narrow, sharply depressed. 



Length of right valve .60 mm. ; height .36 mm. 



Bollia irregularis is probably most closely related to the common Cin- 

 cinnatian form B. persulcata (Ulrich),' with which it agrees in size, gen- 

 eral outline, and distribution of the ridges. Minor differences such as the 

 more pronounced development of the ventral portion of the marginal ridge, 

 and the less bulbous character of the inner ridge, will readily distinguish 

 the Helderberg species. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 21st Bridge. 



Collection. — U. S. National Museum. 



Bollia jugalis n. sp. 

 Plate XCVI, Fig. 19 

 Description. — Carapace obliquely subovate, the anterior end narrower 

 and more abruptly truncate of the two ; ventral margin curved, with the 



' Jour. Cincinnati Soc. Nat. Hist., vol. il, 1879, p. 12, pi. vii, fig. 6. 



