Weller — Kinclerhook Fanned Studies. 105 



POSIDONOMYA? AMBIGUA Will. 

 PI. IV. f. 18-19. 



" Shell of medium size, rather ventricose, somewhat 

 oblique. Hinge-line short, straight, not surpassed by the 

 inconspicuous beak, abruptly rounded at the extremities ; 

 sides of shell subparallel, somewhat straight ; ventral margin 

 circularly curved, gaping at the antero-ventral angle. Cast 

 nearly smooth, but bearing the impression of a few small, 

 irregular wrinkles around the margin. Greatest dimension 

 (from beak to ventral margin), 16 mm. ; anterior-posterior 

 dimension, 14 mm. 



" Three left valves and one right, of an anomalous fossil 

 are here referred with great uncertainty. One of the speci- 

 mens is larger and relatively longer from beak to venter than 

 the one described, and seems to have been everted around 

 nearly the entire pallial border, producing an extensively gap- 

 ing shell. * * * The three valves could scarcely belong 

 to the same species of any genus, but it would be folly to 

 attempt a further discrimination at present." 



Remarks. The above is copied from Winchell's original 

 description of this species. The smaller one of the specimens 

 illustrated is the type of the species, judging from the de- 

 scription and the dimensions given. The larger illustration is 

 of the larger specimen mentioned in the description. The 

 proper disposition of these shells is about as uncertain now as 

 when Winchell wrote his description. The smaller specimen 

 closely resembles the illustration of Paracyclas erecta H.,* 

 from the Chemung group at Warren, Penn., and it may be 

 identical with it. The larger specimen may also be referable 

 to the genus Paracyclas, though it is quite different from any 

 of the recognized species of that genus. A few specimens of 

 a small, nearly flat, smooth, oval shell, having much the form 

 of a Pernopecten ( see p. 85 , pi. III. ,f.5) with the ears removed 

 should possibly be associated with the shells here described. 



* Pal.N. Y. fr.pl. 95. f. 22. 



