306 



Fig. 346. Strepula plantaris. Interior and 

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



Distinouishini^- ChnrHc- 

 ters. — Some \v h a t sole- 

 shaped outline; seini-eir- 

 cular ill front, obli(inely 

 ronnded behind ; broad 

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

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

 standing marginal denticles ; surface with tortuous l)raiich- 

 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. ^ alves wider ])Osteriorly than anteriorly, 

 and impressed with transverse sulci, with raised lobes 

 between. 



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

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



Disthiguishiug Characters. — Multi-lobed with middle lobe 

 isolated and oblique; anterior lobe 

 forked bv vertical sulcus ; posterior lobe 

 similarly, but less deeply, furcate, con- 

 tinuing downward and forward to a 

 swollen portion just at the middle of the 

 ^■entral regi(jn ; 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. 2-48.) (Journ. Cin. 

 Soc. Nat. Hist., Yol. XHI., p. 189, PI. XII. ) 



Dktinguisliing Characters. — Sub-oblong, semi-ovate, inod- 

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



Fig. 247. Beyrichia ham- 

 iltonensis. A left valve, x 

 1.5 (after Jones). 



