The Fauna of the Maxville Limestone. 393 



rounded so that the greatest length of the shell is a little nearer 

 to the ventral than it is to the dorsal margin. Beaks medium, 

 projecting above the hinge line, incurved, and directed anteriorly. 

 Surface covered with rather broad concentric ridges, which near 

 the dorsal margin appear to be in pairs, due to interpolation. 

 Length 38-50 mm.; height 15-22 mm.; width 12-14 mm. 

 The species is characterized by its medium or larger size and 

 by the broad, concentric ridges. 



Horison and locality. — Maxville limestone. 

 Upper zone : Gladstone Mills, Thompson Residence, White 



Cottage. 

 Shale-nodular zone: Stimmel Residence, Maxville. 

 Undetermined zone : Middle of Cut No. 6, Mt. Perry- Fulton- 

 ham. 



ALLORISMA MAXVILLENSIS— Whitfield. 



1882. Allorisma Ma.vvillensis. Whitfield, Ann. N. Y. Acad. Sci., Vol. 

 II, p. 222. 

 Maxville limestone : Newtonville, Ohio. 

 1891. Allorisma Maxvillensis. Whitfield, Ann. N. Y. Acad. Sci., Vol. 

 V, p. 588, pi. 14, figs. 7, 8. 

 Maxville limestone: Newtonville, Ohio. 

 1895. Allorisma Maxvillensis. Whitfield, Geol. Surv, Ohio, Vol. VII, 

 p. 475, pi. 10, figs. 7, 8. 

 Maxville limestone : Nevi^tonville, Ohio. 



Description. — • "Shell small, the specimen used being a little 

 less than one inch in length and the height less than half the 

 length. Form of the shell transversely elongate, and cylindrically 

 ■oval, the cardinal and basal margins parallel and very slightly 

 curved, and the extremities very nearly equally rounded; beaks 

 small, inrolled, barely projecting above the cardinal line, and 

 situated at about one-fourth of the entire length from the anterior 

 •end. Body of shell very evenly and highly rounded from the 

 cardinal to the basal margins, and almost as convex posteriorly 

 as in front. Umbonal r»dge scarcely perceptible, and the 

 umbonal slope convex ; escutcheon and lunule not defined ; 

 anterior slope abruptly rounded. Surface of the shell marked 



