Bracldopoda of the Cincinnati Group. 15 



beneath the beak of the other valve ; dorsal valve very convex in the 

 middle and posterior regions, and depressed anteriorly ; beak pointed 

 and projecting beyond the opposite valve. 



Outer shell of l^oth valves very thin and smooth about the beak and 

 unibonal regions, but regularly punctate on other parts in lines radia- 

 ting to the margins. Where the nonpunctate shell is exfoliated, no 

 radiating strise or punctate structure is visible ; l)ut where the punctate 

 shell is exfoliated, the inner shell, to the unaided eye, appears to be 

 marked by regular radiating striee, with fine puncta between them. 

 A magnifier, however, shows the radiating stride to be only the lines 

 between the furrows, produced by the punctate structure. 



Length of the largest specimen known to me, 0.82 inch ; width, 0.84 

 inch; convexity, 0.22 inch. 



This specimen may belong to a new species, so I have referred it to 

 Conrad's species, with a doubt. It is rare and its range unknown. 



Trematls (.?)/fosa— (Hall, 1347). 



Shell orbicular; dorsal valve very convex, greatest convexity in the 

 central part and sloping in all directions ; beak marginal ; surface 

 radiated with numerous, fine, elevated, thread-like strise, which are alike 

 visible on the exterior and interior part of the valve ; strife increased 

 by intercalation. Interior marked by two rather large, subcircular, 

 muscular impressions, situated a little anterior to the beak, and sepa- 

 rated by the median line. Ventral valve unknown. 



Length of a large specimen, 0.54 inch; width, 0.56 inch; convexity, 

 0.30 inch. 



Found on the hills back of Cincinnati, and at many other places, 

 ])ut its range is not very definitely known. Good specimens are quit(i 

 rare. 



This species evidently belongs to a new genus or a sub-group under 

 the o-enus Trematls. The character of the two muscular impressions, 

 and the absence of the punctate structure in the outer shell, that 

 characterizes both the terminalls and mlllepunctata, must separate this 

 species, at least, subgenerically, from all other shells found in the Cin- 

 cinnati Group. 



For Trematl>i Dyeri—(S. A. Miller), see vol. 1, page 347, of 

 this Journal, October, 1874. 



