is formed on the cardinal and posterior ends. This surface on the 

 posterior side is somewhat depressed and set off by angles, thus form- 

 ing a large "lunule" which is very sharply defined. Nothing at all 

 comparable to this is developed on the cardinal plane. 



The surface is marked by very fine, regular, concentric striae. 



This species resembles several that occur in such different strati- 

 graphic and geologic relations that I would hesitate to regard them 

 as the same without conclusive evidence of very close agreement. 

 It is similar to the Mississippian N. shumardiana, but it is rather 

 less elongated transversely, and it is readily distinguished by its higher 

 convexity and more prominent umbones. N. wewokana, N. levati- 

 formis var. obliqua, and N. pulchella are related but distinct species." 



Remarks. N. lunulata is common in the Sharon ore at one 

 locality in Scioto County where it is associated with N. subrotundata 

 Girty mss. and N. elongata n.sp. It occurs only as internal casts. 



Horizon and locality. Sharon ore: Lick Run, Scioto County 

 (Locality 2), c. 



Nucula beyrichi von Schauroth 



1866 Nucula beyrichi. Geinitz, Garb, und Dyas in Nebr., p. 21, tab. 1, Figs. 36, 37. 

 Coal Measures: Nebraska City, Nebraska. 



This small Nucula is rare in the rocks of Pottsville age in Ohio 

 and is represented in the collections studied by only a few individuals 

 from the Harrison ore and the Lower Mercer and McArthur lime- 

 stones. A single example has been found from the Harrison ore in 

 the form of an internal cast, which, however, is so well preserved 

 that it is referred to this species with some confidence. 



Horizon and locality. Harrison ore: Jackson County (Locality l),r. 



Genus Nuculopsis Girty 

 Nuculopsis ventricosa (Hall) 



1858 Nucula ventricosa. Hall, Geol. Iowa, Vol. 1, Pt. 2, p. 716, PL 29, Figs. 4, 5 a,b. 



Coal Measures: Iowa. 

 1915 Nuculopsis ventricosa. Girty, U. S. Geol. Surv., Bull. 544, p. 117, PL XV, 



Figs. 1-8. 



Wewoka formation. Oklahoma. 



Nuculopsis ventricosa occurs in the basal member of the Potts- 

 ville and ranges throughout the entire formation, although individ- 

 uals are by no means common. It is most often found in the Lower 

 Mercer and McArthur members. In the Harrison ore it is associated 

 with N. subrotundata Girty mss., and in the Sharon ore also with 

 N. lunulata Girty mss. and N. elongata n.sp. A considerable varia- 

 tion exists in the size of the individuals; a specimen of average size 

 from the Sharon ore measures: length 9.2 mm., height 7 mm., thick- 

 ness of a single valve 3.5 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 1), r. Sharon ore: Lick Run, Scioto County (Locality 2), r. 



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