248 



PROCEEDINGS OP THE ACADEMY OF 



external characters at least, referred it to Pleurophorus costaim, Brown, (sp.) 

 Indeed it seems to be as nearly like Prof. King's principal figure of that 

 species, (f. 13, pi. xv, Perm. Foss. of England,) as any other individual speci- 

 men could possibly be expected to be, and more nearly like it than any other 

 figure of that shell we have ever seen. Nevertheless, from the different 

 horizons occupied by these shells, we have scarcely a doubt that, if we could 

 see the hinge and interior of that now before us, good specific differences 

 would be observable. 



Locality and position. Keokuk division of the subcarboniferous series, 

 Warsaw, Illinois. 



Genus GRAMMYSIA, De Verneuil, 1847. 



GkAMMYSIA ? RHOMBOIDALIS, M. & W. 



Shell rather large, very gibbous, presenting a rhombic form as seen in a 

 Bide view, and a distinctly cordate outline as seen in an anterior or posterior 

 view; umbonal slopes extremely prominent and very oblique ; beaks nearly 

 terminal, approximate at their points, rising above the hinge line, and dis- 

 tinctly curved inwards and forwards ; anterior and antero-ventral regions im- 

 mediately in front of the oblique umbonal ridge, abruptly contracted, with a 

 broad undefined depression extending from the front part of the beaks obliquely 

 to a point near the middle of the base ; dorsal region between the umbonal 

 ridge^ and the cardinal margin, a little concave near the beaks. Posterior 

 margin obliquely truncated with a moderately convex outline to the posterior 

 basal extremity, which is subangular, or very narrowly rounded ; base rather 

 long, a little convex in outline behind the middle, and straight or slightly 

 sinuous just in front of it, but rounding obliquely upward anteriorly. Anterior 

 side (which is imperfect in our specimen) short, or apparently scarcely pro- 

 jecting beyond the beaks, more or less obliquely rounded and somewhat gap- 

 ing ; cardinal margin (judging from casts) rather short, and inflected so as to 

 form behind the beaks a distinctly defined, rather wide depression or es- 

 cutcheon. Surface, as near as can be determined from casts, ornamented with 

 small, regular concentric ridges. Hinge, muscular and pallial impressions 

 unknown. 



Length, about 3-55 inches ; height, 2-06 inches ; greatest breadth (near the 

 middle of valves), 2-42 inches. 



The most marked peculiarities about this shell, are the remarkable promi- 

 nence and obliquity of its umbonal ridges, which near the beaks stand out 

 as if compressed antero-posteriorly, and the nearly terminal, obliquely in- 

 curved character of the beaks. The specimen is not in a condition to show 

 whether or not it has a distinct lunule in front of the beaks, but we suspect 

 that it has. In some respects it resembles in form Ci/rtodonta Hindi of Billings, 

 from the Cincinnati group, or so called Hudson riverbed of Canada, but diflers 

 in having its umbonal ridges so much more prominent as to give greater con- 

 vexity to the valves ; while its umbones, although more prominent, are much 

 narrower in their antero posterior diameter. More important differences, 

 howeve^ are the presence of a broad undefined sulcus extending obliquely 

 from the anterior side of the beaks of our shell, to near the middle of its base, 

 and the apparent slightly gaping character of its anterior side. Notwithstand- 

 ing the general resemblance of these forms, there can be little doubt but they 

 really belong to distinct families, since the Canadian shell doubtless belongs 

 to the Arcidw, Avhile that before us appears to be related to the Anatinidce. 



Although we have placed our shell provisionally in the genus Grammysia, 

 we strongly suspect that when its hinge and interior can be seen, it will 

 be found to be either generic-ally or subgenerieally distinct from G. hi sulcata, 

 Con. sp., the type upon which that genus was founded. At any rate, it dif- 

 fers materially in form, and the prominence of its umbonal ridges, as well as 



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