DESCRIPTION OF SPECIES 269 



peculiar pitted surface on the Nebraska form, described by Professor 

 Geinitz as 0. cribrosum, is not apparent on the Ohio specimens, but 

 this difference is in no way significant as the pitted character was prob- 

 ably produced by minute parasites and therefore is not of specific im- 

 portance. 1 



Horizon and locality. -Lowell ville rmmbar: Muskingum County, 

 Localities 19, 21, c. Boggs member: Muskingum County, Localities 

 26, 28, c. Widely distributed throughout the Lower Mercer and 

 McArthur members, c. 



Genus Coloceras Hyatt 

 Coloceras sp. 



Remarks. A small imperfect specimen from the Sharon ore has 

 been referred to the genus Coloceras, although the generic relationships 

 are very doubtful. Several larger, more perfect specimens from the 

 McArthur limestone have been assigned to the same genus with more 

 confidence, although specific determination seems impossible. How- 

 ever, the forms from the Sharon and McArthur horizons seem closely 

 related. 



Horizon and locality. Sharon ore: Scioto County, Locality 2, r. 

 McArthur limestone: Jackson County, Locality 80, r; Hocking County, 

 Locality 86, r. 



Genus Metacoceras Hyatt 



Metacoceras pottsvillensis n. sp. 

 PI. XVI, figs. 7, 8 



Description. Shell about median in size, consisting of a little 

 more than two closely coiled volutions which increase rather gradually 

 in size. Whorl section subquadrate, a little wider than high, the dimen- 

 sions near the living chamber being: width 26 mm., height 21.5 mm. 

 Ventral surface very slightly convex; sides flattened and converging a 

 little toward the ventrilateral shoulders; impressed zone of dorsum 

 about 15 mm. in width, deeply concave, forming a sharply acute angle 

 along the median line; sides of dorsum between impressed zone and 

 umbilical shoulders broad, slightly convex; umbilical shoulders sharply 

 angular, forming widest portion of volutions, situated about one-third 

 the distance from the dorsal edge to the ventrum; ventrilateral shoulders 

 angular, marked by prominent highly elevated nodes which are situ- 

 ated opposite each other on either side of the ventrum, 15 to 17 mm. 



Meek, F. B., U. S. Geol. Surv. Nebr., p. 234, 1872. 



