Weller — Kinderhook Fanned Studies, 165 



differs from that species in its smaller size and in its more 

 extended hinge-line. 



Spirifer marionensis Shum. 



PL XIV. f. 1-2. 



The specimens of this species in the upper yellow sand- 

 stone are not common, but those that have been observed are 

 indistinguishable from specimens in the superjacent oolite 

 bed where the species becomes much more abundant. 



Spirifer peculiaris Shum. ? 



Fl. XIV. f. 6-9. 



Shell subcircular to longitudinally subsemielliptical in 

 outline. Length of hinge-line usually less than the width 

 of the shell in front, the cardinal extremities usually 

 rounded. Valves subequally convex. Greatest convexity 

 of pedicle valve posterior to the middle of the shell ; beak 

 small, pointed and incurved; umbo prominent; sinus nar- 

 row, sharply defined near the beak, but becoming less dis- 

 tinct and relatively shallow anteriorly, in the casts often 

 ill defined throughout, and sometimes indicated only by 

 a flattening of the shell along the median line; cardinal 

 area concave, its margin rounded in the casts. Brachial 

 valve regularly convex, fold but slightly elevated above the 

 general surface of the shell. Lateral slopes of each valve 

 marked by six to eight simple, depressed, rounded plications 

 which decrease regularly in size from the fold and sinus to 

 the lateral margins ; in the casts the plications are often ob- 

 solete or nearly so; the fold and sinus without plications. 



A rather large cast of a pedicle valve measures 16 mm. io 

 length and 19 mm. in width. If the shell were preserved,, 

 the length would be increased considerably, much more in 

 proportion than the width. Most of the specimens from the 

 upper yellow sandstone are smaller than the one whose di- 

 mensions have been given, the length of the shell usually 

 being less than 15 mm. 



Remarks. The only specimen observed which preserves 

 the external features of this shell is a wax impression taken 

 from a natural mold in the University of Michigan collec- 

 tion. In this specimen the hinge-line is somewhat longer 



