Contributions to Invertebrate Palaeontology, SSY 



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 couiited 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 F. Jiexicostata McCoy, from the English Carboniferous 

 rocks (British Pal. Foss., p. 499, pi. 3, E, figs. 11-13), is very simi- 

 lar, but has slightly stronger radii, is somewhat broader, and differs 

 in having a longitudinal depression just below the hinge-line, whicli 

 this species does not possess. 



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

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



Genus SCHIZODIJS King. 



Scliizodiis Cliestereiisis. 



Plate XIV, fig. 4. 



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



Shell of medium size, transversely subovate in outline, 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, whicli is near the middle of the height, 

 and rounding backward below ; posterior 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 labelled by him with the name here applied to it. 

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

 present condition very closely 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. 



For^mation and Locality — In the Maxville limestone, at Max- 

 ville, Ohio. Collection of Columbia College. 



