Flo. 246. Strepula plant axis. Interior and 

 exterior of a left valve, x 25 (after Jones). 



;;<><; 



Distingu ish ing ( 1m ra < •- 

 ters. — Somewha 1 sole- 

 shaped outline; semi-cir- 

 cular in front, obliquely 

 rounded behind : broad 

 hinder end, with thin flat lip-like margin, bearing about ten 

 obscure shallow pits; narrow front end. with six strong out- 

 standing marginal denticles : surface with tortuous branch- 

 ing ridge. 



Found in the ''Hamilton group, at Eighteen Mile Creek, 

 Lake Erie, N. Y." (Jones.) 





Genus BEYRICHIA. McCoy. 



[Ety. : Proper name.] 

 (1844: Synop. Sil. Foss. Ireland, p. 57.) 



Carapace with equal oblong convex valves, their extrem- 

 ities rounded, their ventral border semi-circular, and dorsal 

 border straight. Valves wider posteriorly than anteriorly, 

 and impressed with transverse sulci, with raised lobes 

 between. 



Beyrichia iiamiltoxexsis. Jones. (Fig. 247.) (1890: 

 Quart, Journ. Geol. Soc, Vol. XLVL, p. 19. ) 



Distinguishing Characters. — Multi-lobed with middle lobe 



isolated and oblique; anterior lobe 

 forked by vertical sulcus : posterior lobe 

 similarly, but less deeply, furcate, con- 

 tinuing downward and forward to a 

 swollen portion just at the middle of the 

 ventral region: granulose surface, with 

 some of the granules sharp and prickly at the dorsal region. 

 Found in the Hamilton group, Eighteen Mile Creek. Lake 

 Erie Shore. (Jones. ) 



Beyrichia tricollina. Ulrich. (Fig. 248.) (Journ. Cin. 

 Soc. Nat. Hist.. Vol. XIII., p. 189, PI. XII. ) 



Distinguishing Characters. — Sub-oblong, semi-ovate, mod- 

 erately convex valves, with a long straight hinge line, and 



Fig. 247. Beyrichia ham- 

 Utonensis. A left valve, x 

 15 (after Jones). 



