251 



Fig. 166. M<>(Uomor]}ha siib-alata. Three right \^ 

 variations ifroin Hall). 



me left valve, showing 



abundance) ; in the Trilobite beds and the shales above, at 

 Section 8, and on tlie Lake Shore (common); and in the 

 Plenrodictynm beds (rare). 



MoDiOMoRPHA ALTA. (Conrad.) (Fig. 167.) (Pal. X. Y., 

 Vol. v., Ft. 1., p. 278, Fls. XXXVIL. LXXX. ) 



Distinguishing ChavRcters. — Broad rhomboid-ovate out- 

 line; curved posterior marg-in ; elevated ])Osterio-dorsal 



Fig. 167. Modiomorpha alia. Right and left valves of diffei-ent individuals (from Hall). 



portion ; ])roduced. rounded, but ill-defined, antei'ior portion ; 

 irregular surface striae. 



Found only in the middle Pleurodictvum bed, in Avery's 

 Ravine (rare). 



Gexls GOXIOPHOPvA. Phillips. 



[Ety. : Oonia, an angle; pJtorox, bearing.] 

 (1848: Memoirs Geol. Snrv. Gt. Britain, Vol. II., Pt. L, p. 264.) 

 Shells with equal, but very inequilateral, valves, rhom- 

 boidal or trapezoidal in outline, obliquely truncate behind, 



