DESCRIPTION OF SPECIES 259 



Description. Three fragments of Zygopleura are among the col- 

 lections at hand, two from the Lower Mercer and one from the McArthur 

 limestone. The latter has approximately the same number of costae 

 on the whorls and probably an equal number of whorls as Herrick's 

 species, Loxonema plenum, although accurate comparisons cannot be 

 made owing to the imperfect condition of the specimen. The Lower 

 Mercer specimens which occur in the form of external molds, are re- 

 ferred to the same species with much less confidence. The costae are 

 coarser than those of Herrick's species, which judging from his figure 

 has about twenty to a volution, while the specimens under discussion 

 are estimated to have only about sixteen to eighteen to a volution. 

 The whorls are somewhat less convex, and the number of volutions 

 considerably more than Herrick's in comparison to the size of the shells. 

 Although these differences may be overestimated as our specimens 

 are imperfect, nevertheless it does not seem at all unlikely that our 

 forms constitute an undescribed species, but for want of more and 

 better specimens, they are for the present provisionally placed with 

 Z. plenum. 



Horizon and locality. Lower Mercer limestone: Perry County, 

 Somerset, Locality 35, r; Muskingum County, near Fairview School, 

 Locality 45, r. McArthur limestone: Vinton County, Moore mine 

 near McArthur, Locality 84, r. 



Zygopleura plicata (Whitfield) 



1882 Loxonema plicatum. Whitfield, Ann. N. Y. Acad. Sci?, Vol. 2, p. 231. 



Coal Measures: Carbon Hill, Hocking County, Ohio. 

 1891 Loxonema plicatum. Whitfield, Ann. N. Y. Acad. Sci., Vol. 5, p. 601, PI. 15, 



Figs. 14, 15. 



Coal Measures: Carbon Hill, Hocking County, Ohio. 



Description. An external mold of a small, very slender, high- 

 spired gastropod from the Lower Mercer limestone belonging to the 

 genus Zygopleura has been referred with some doubt to the above 

 species. The apical angle and the width of the volutions are similar 

 to those of Z. plicata, while the surface is marked by fourteen to 

 sixteen vertical plications. The spire is high and consists of about 

 twelve volutions. An external cast also from the Lower Mercer lime- 

 stone has been referred to the same species with more confidence, al- 

 though in size it is less than two-thirds that of Whitfield's form. How- 

 ever, no other essential differences could be noted. 



Horizon and locality. Lower Mercer limestone: Perry County, 

 Somerset, Locality 35, r; Licking County, Flint Ridge, Locality 47, r. 



