248 

 Genus PLETHOMYTILUS. Hall. 



[Ety. : PletJto. to be full ; rnytilus, a geuus.] 

 (1884 : Pal. X. Y., Vol. V., Pt. I., p. 14.) 



Shell with etjiial gibbons valves, of an outline reseml»liiig 

 Mvtiliis, and having a finely striated ligamental area, which 

 extends across the shorter or transverse diameter of the 

 valve. Height greatly exceeding the length. The posterior 

 side is slightly winged. Small, oblique, lateral teeth are 

 present, but no cardinal teeth have been observed. Test 

 with concentric sti'ite. 



Plethomytilus oviFoimis. (Conrad.) (Fig. 163.) (Pal. 

 N. Y., Vol. v., Pt. 1., p. 255, Pis. XXXI., LXXXYH. ) 



Distinguishing Cliaracters. — Large size; ovate ontline; 

 beaks projecting above the cardinal line: truncate trout, 



Fig. 163. Plethomiitit'i.< nnhnnus. 

 valve, with attenuated beak (from Hall;. 



Left valve, showing: striated hinge area : right 



with small fissure for the passage of the byssus; wide liga- 

 mental area. 



Found only in tlie upper part of the Encrinal limestone, at 

 the lower end of Section 5 (common). 



