OF DEMSON UNIVERSITY. 



45 



cardinal area arched, striate parallel to the hinge line, foramen }{ to 

 1-5 as wide as the hinge; mesial sinus rather narrow and ill-defined, 

 triangular in section, continuing to the beak ; interior with short, di- 

 verging dental lamellae and small rostral cavity. Dorsal valve quite 

 flat, except the rather low, ill-defined, triangular fold ; beak projecting 

 beyond the hinge-line; area narrow, striate af right angles to hinge-line. 

 Surface of both valves covered by numerous small, low, rounded cos- 

 tae, which bifurcate somewhat irregularly and are marked by numer- 

 ous radiating slrice and, less obviously, by concentric striae as well as 

 the usual lines of growth. (The cancellated appearance spoken of 

 by Meek is rarely observed, while the radiating striations are quite 

 noticeable. Sixty-five to seventy-five costje are found on a valve of 

 medium size, from eight ^o fifteen occupying fold and sinus. The 

 typical form is found near the summit of the Waverly, about loo feet 

 above congl. II, with Productus seniireticulatus. This layer occurs at 

 at the very top of the exposure at Rushville and cannot be far below 

 the Chester limestone. 



In conglomerate I, are found specimens apparently intermediate 

 between the previous species and S. striatiformis, but more convex than 

 either. In the free stone still above is another variety which is with 

 less doubt referred to S. striatiformis. Specimens are figured on Plate 

 VI, Figs. 6, 7. These have a broader sinus and more nearly (lu.ulr.itL- 

 form, though short mucronate ears are retained. 



If S. centronataisa valid name for the form from Cuyahoga .shales 

 the relation between that species and S. marionensis must be left for 

 future study. The close relation of all these to S. disjuncta of the Che- 

 mung is noteworthy. 



Spirifer hij)J Irahn 



n.iu. 



"^QX. Spirifer bipHcatus, Mkkk, (). I'al. \ Ol H. 



But a single dorsal valve has been encountered with the characters 

 of S. biplicatus, indeed, we susi)ected the validity of the species. It 

 may be confessed that a wider range of observation may invalidate the 

 assumed distinctions. This dorsal valve differs from those of S. stri- 

 atiformis, with which it is associated, in the greater distinctness of the 

 plicjK, and the depressions bordering the median fold, and by the fact 

 that the plicae on the fold are so much smaller than those of the rest 



