259 



Distinguishing Clinrarters. — Deeply sinuate or emarginate 

 posterior marg-in; strong nmbonal ridge, Avitli depression 

 above it; produced post-cardinal extremity; strong, ele- 

 vated, distant, lamellose, concentric ridges, with finer strite 

 between. 



Found in the Lower shales, down to twenty-five feet below 

 the Encrinal limestone, at Sections 5 to 7 (common); also 

 in the shale below the Nautilus bed, in Aveiw's Creek. 



Genus MACRODON. Lycett. 



[Ety. : Macros, long ; odous, tooth.] 

 (1845: Murch. Geol. Chelt.) 



Shells with equal inequilateral valves, which are trans- 

 versely sub-elliptical, or sub-ovate, in outline. The anterior 

 end is angular at the cardinal line and rounded below. The 

 posterior end is rounded or obliquely sub-truncate. Beaks 

 anterior to the middle; cardinal line long and straight. 

 Ligament external. Cardinal teeth several; lateral teeth 

 two to four, situated near the extremity of the cardinal line. 

 Surface marked b}' concentric stri^, which are often lamellose, 

 and in some species by fine radiating lines. 



Macrodox hamiltonli:. Hall. (Fig. 178.) (Pal. N. Y., 

 Vol. Y.,Pt. L, p. 349, PL LL) 



Distinguishing Cimracters. — Obtusely sub-angular ends 

 of hinge line ; rounded post-inferior end ; strong, distant 



Fig. 178. Macrodonhamiltonice. A right valve ; a specimen retaining both valves, the 

 shell exfoliated (from Hall;. 



lamellose concentric lines ; fine interrupted radii, strongest 

 on the posterior part of the shell. 



