COAL-MEASUKE SPECIES. 336 



At a first glance this shell recalls Macrodon tenuistriatus, M. and W., 

 (111. Report, v., 576, pi. XXIII., figs. 4a, 6), but it is a much larger, decid- 

 edly less gibbous shell, and appears to be entirely without the minute, 

 crowded, radiating striae seen on the central and anterior portions of that 

 species. This absence of radiating markings on its central and anterior 

 portions will also distinguish it from M. carbonarius (=Arca carbondria, 

 Cox), Kentucky Geol. Rep., Atlas, pi. VIII., fig. 5), which has well defined 

 radiating costa3 all over. 



Locality and position : The original type specimens of this species were in the lower 

 part of the Coal Measures in Monongahela county, We&t Virginia, while the specimen 

 here figured came from the Coal Measures at Newark, Ohio. Eev. Mr. Hertzer's col- 

 lection. 



Genus YOLDIA, Moller, 1842 

 (Kroyer's Nat. Tidsskr., IV., 91.) 



YoLDiA Stevensoni, Meek. 



Plate 19, figs. 4a, 6. 



Yoldia Stevensoni, Meek (1871) ; List Carb. Fobs, from West Virginia, 6 (Ext. from Eep. 

 Regents University of West Virginia). 



Shell much compressed,very thin, longitudinally elliptic- subovate, being 

 about twice as long as high, with the widest part a little in advance of 

 the middle; anterior margin narrowly rounded ; posterior narrower and 

 more compressed than the anterior; basal outline broadly semiovate, 

 being a little more prominent anteriorly; cardinal border sharply cari- 

 nated, and provided with a marginal furrow on each valve, slightly con- 

 vex in outline anteriorly, and straight or a little concave behind the 

 beaks; umbonal slopes not angular; beaks depressed and placed very 

 slightly in advance of the middle. Surface ornamented by fine, regular, 

 concentric lines, separated by wider furrows. 



Length, 0.78 inch; height, 0.38 inch; convexity, 0.16 inch. 



This is a very neat, remarkably compressed species, having exactly 

 the form and external appearance of a true Yoldia, but its hinge and 

 interior are unknown. The specific name was given in honor of Prof. 

 John J. Stevenson, of New York, late of the University of West Virginia. 



Locality and position : The figured specimen was from Monongahela county, West 

 Virginia, found in a dark shale just below the Mahoning sandstone. 



