WAVEELY GROUP SPECIES. 309 



nearly central, or located a little in advance of the middle, depressed 

 nearly to the horizon of the dorsal line behind them ; posterior umbonal 

 slopes sub-angular near the beaks, but becoming more prominently 

 rounded along a line between the posterior basal extremity and the um- 

 bonal region; ligament apparently extending nearly the whole length 

 of the cardinal margin behind the beaks, more or less prominent exter- 

 nally, but apparently extending rather deeply between the margins all 

 the way along. Surface with moderately distinct ridges and furrows of 

 growth, most clearly defined on the anterior slope, where they seem to 

 be somewhat interrupted by obscure traces of radiating furrows. 



Length, about 6.90 inches; height, about 2.22 inches; convexity, 1.60 

 inches. 



This fine species is intermediate in its characters between P. nasutus, 

 Meek, and P. Missouriensis, Swallow. It differs from the latter, however, 

 in having its beaks more nearly central, and its posterior dorsal margin 

 proportionally shorter, as well as in having its anterior dorsal margin 

 more concave in outline, and its posterior umbonal slopes decidedly less 

 angular. The farther anterior position of its beaks, and its obtusely 

 rounded umbonal slopes, also readily distinguish it from P. nasutus. 



I originally placed this group as a subgenus under Sanguinolites of 

 McCoy; but it is more probably distinct generically from that group, 

 though this question can never be positively decided until the hinge of 

 these shells, and that of Prof. McCoy's type, can be known and compared. 

 The species here described is named in honor of Prof. E. B. Andrews, of 

 the Ohio Geological Survey, who discovered the typical specimen. 



LocaHVy and position : Sciotoville, Ohio. Waverly group of the Lower Carbonif- 



Genus ALLORISMA, King, 1844. 

 (Mag. Nat. Hist., XIV, 316.) 



Allorisma (Ceecomyopsis) pleueopistha, Meek. 



Plate 13, figs. 4a, 6, c. 



Allorisma (Sedgwickial) plewopistha, Meek, (1871), Proceed Acad. Nat. Sci., Philad., 

 XXIII, 14. 



Shell depressed and elongated, or more than twice as long as high, 

 moderately convex centrally and anteriorly, and attenuated and produced 

 behind ; pallial margin long, nearly straight along the middle, rounded 

 up anteriorly, and ascending more gradually behind ; posterior side very 

 narrow, truncated and somewhat gaping at the extremity, which meets the 



