474 GEOLOGY OF OHIO. 



MOIXUSCA. 



LAMELLIBRANCHIATA. 



Pinna Maxvillensis. 



Plate X, fig. 5. 



Pinna Maxvillensis Whitf., Ann. N Y., Acad. Sci., 1882. p. 221. 



Shell of about a medium size, very acutely triangular in outline, -with highly 

 convex valves ; the length along the hinge equal to nearly three times the greatest 

 width. Hinge-line straight, not quite as long as the shell below ; anterior end 

 acute; basal margin very slightly arcuate, and the posterior extremity rather 

 broadly rounded; the point of greatest length being at about one-third of the width 

 below the hinge-line. Surface of the shell, except for a short distance within the 

 basal margin, marked by moderately strong, simple radiating plications, about 

 eighteen in number, as counted at the posterior end of the specimen figured, but 

 increasing in number with increased growth; the additions being near the hinge. 

 There are also numerous strong concentric lines of growth parallel to the margin, 

 often forming undulations of the surface. 



I find no American species described that closely resembles this one; 

 but P. jiexicostata McCoy, from the English Carboniferous rocks (British 

 Pal. Foss., p. 499, pi. 3, E, figs. 11—13), is very similar, but has slightly 

 stronger radii, is somewhat broader, and differs in having a longitudinal 

 depression just below the hinge-line, which this species does not possess. 



Formation and Locality. — In the Maxville limestone, at Maxville, 

 Ohio. Collection of Prof. E. B. Andrews. 



Genus SCHIZODUS King. 

 SCHIZODUS CHESTEREXSIS. 

 Plate X, fig. 4. 

 Schizodus Chesterensis M. and W., Geol. Rept. Ills., vol. 2, p. 301. pi. 23, fig. 6. 



Shell of medium size, transversely subovate, with moderately convex valves 

 and large, strong, incurved, and projecting beaks. Anterior end forming one-third 

 the length of the shell, inflated, and rapidly sloping from the beaks to the longest 

 point, which is near the middle of the height, and rounding backward below; pos- 

 terior end elongated and narrowed, obtusely pointed at the extremity ; basal margin 

 irregularly convex, most strongly arcuate opposite the beaks; posterio-cardinal 

 margin sloping somewhat rapidly from the beaks backward, and the cardinal slope 

 rather abrupt. Surface of the shell smooth, except for the fine lines of growth. 



The specimen used in the above description was identified by Mr. F. 

 B. Meek, and labeled by him with the name here applied to it. The 

 specimen is slightly distorted and otherwise injured, but in its present 

 condition very closefy resembles those described in the Illinois Report. 

 Still on one valve which preserves nearly all of the posterio-cardinal slope, 

 the lines of growth would indicate a shell with a much higher posterior 

 end than those above cited: and when better material is obtained it may 

 be necessary to give it another specific name. 



Formation and Locality. — In the Maxville limestone, at Maxville, 

 Ohio. Collection of Columbia College. 



