244 



Found four feel below the base of the Trilobite beds, in 



Avery's ("reek (rare) : and veryrarelyin 

 the shale between the Nautilus and 

 Strophalosia beds. 



Pterinopecten undosus. Hall. 

 I Fig. 158.) (Pal. N. Y., Vol. V., Pt. I., 

 p. 72, Pis. II., LXXXII.) 



Distinguishing Characters.— Lengi 1 i 

 greater than height; short hinge line; 

 concave margins of ears and wing; 

 sharp, crenulated striae; concentric un- 

 dulations; deep byssal notch of right 



Fig. 158. Pterinopecten un 

 dosus. Small specimen, pre- i v 



serving both valves, and show- \ <ti \ c. 

 ing strong undulations cfi'om 

 Hall). 



Found (?) in the Demissa bed (rare). 



Genus PTERIXEA. Goldfuss. 



[Ety. : Pteron, a wing.] 

 (1826: Peter fact. Germ.) 



Valves unequal, left valve most convex. The shell is very 

 oblique, the wing large, and the ear small. Two or more 

 cardinal teeth and linear oblique lateral teeth occur. The 

 hinge line is straight, and has a linear flattened marginal 

 cartilage facet, which is longitudinally striated. The sur- 

 face of the shell is ornamented by rays. 



P T E R I X E A F L A 15 E L L A . 



(Conrad.) (Fig. 159.) (Pal. 

 \. Y., Vol. V., Pt, I., p. 93, 

 Pis. XIV., XV., LXXXIII.) 



Distinguishing f 'haracters. 

 — Large size; convex left 

 valve and flat or concave 

 right valve; large, well-de- 

 fined, triangular wing, with 

 concave margin: small, 

 rounded, well-defined ear; 



FlG 15fl I'terinen flttli-lld. Lefl valve -, -, -■ • . , 



CfromHaii). stronu - . rounded, distant 



