178 Systematic Paleontology — Middle De:\^oxian 



gently dofincfl below the middle of the shell. Dorsal valve much more 

 convex than the ventral, the greatest gibbosity a little above the middle, 

 the center elevated in a broad mesial fold. Surface marked by niimerous 

 rounded or subaugular plications, of which from three to seven are de- 

 pressed in the sinus and a corresponding number elevated on the fold, the 

 plications of the fold and sinus bifurcate, while those of the sides are 

 simple or obscurely bifurcating, and all usually become obsolete at one- 

 third to one-fourth the length of the shell from the apex ; concentrically 

 marked by raised thread-like striae. 



In the arenaceous shales of the Eomney formation and above the fissile 

 black shales, are specimens of Liorliynclius which are not much larger 

 than those from the black shales, but are marked by somewhat coarser pli- 

 cations. These specimens are never abundant and they have been referred 

 to L. laura, although most of them are smaller than the figured specimens 

 of that species. 



Length, 8-13 mm.; width, 9-13 mm. 



Occurrence. — Romkey roRMATiON, Hamilton Member. Williams 

 Road, 3^ miles southeast of Cumberland; east bank Evitts Creek below 

 Wolfe Mill. 



Collections. — Maryland Geological Survey; New York State ]\Iuseum. 



LlORHYNCHUS cf . MYSIA 



Plate XV, Figs. 13-17 

 Leiorhynchus mijsia Hall, 18G7, Pal. N. Y., vol. iv, p. 357, pi. Ivi. figs. 1-5. 



Description. — "Shell small, suboricular; valves subequally convex, 

 with a few strong plications reaching half way from the margin to the 

 beak of the shell. This species is distinguished by its small size, circular 

 form, and proportionally much stronger plications, of which there are at 

 least three on each side of the fold and sinus, terminating near the middle 

 of the shell. In a few larger individuals, the plications near the middle of 

 the shell have a greater extent. A single plication marks the sinus. The 

 length of the shell is usually less than three-eighths of an inch ; width a 

 little greater. One individual measures nearly a quarter of an inch in 



