48 Bulletin 31 48 



of this species consist of a large number of radiating lines crossed 

 and crenulated by fine conceneric lines (compare figs. 6 and 11). 

 As the shell grows older, there is a slight tendency for the radiat- 

 ing lines to group themselves in broad, faint ribs, but in the adult 

 stage the exterior of the shell lacks the moderate ribbing of stam- 

 inca and appears very nearh' smooth. Different weathering and 

 stages of decortication bring out different faint radiating features, 

 — fine lines especially. The internal crenulations of the margin, 

 however, show about 60 crenulce in place of about 80 in like sized 

 specimens of staminea. 



This species is perhaps one tenth part as abundant in the 

 Claiborne sands as staminea. But, strangel}- enough, as one 

 leaves that locality or descends into lower stages it is clearly the 

 idonea stock that prevails. As already stated in these Bulletins, 

 (11, p. 242) it is very doubtful whether the specific name idonea 

 ought to be used for the Lignitic or Sabine forms ; as it will be 

 seen b}^ consulting pi. 14, figs. 5 and 6, that they are too erect, 

 and show ribbing far too distinctl3^ The early Eocene forms re- 

 corded in the Maryland State Survey publications, (Eocene, pi. 5 1 , ) 

 are a little more oblique than the earl}^ Gulf representatives, but 

 still show the Sabine stage ribbing. On the other hand, the vast 

 numbers of representatives from the Orangeburg District, S. C, 

 seem no better ornamented exteriorly than the Claiborne sand 

 forms and are even more pointed or angular in appearance. 

 There seems to be no reason whj^ the latter maj' not be referred 

 to a mutation of idonea. 



Type. — Phila. Acad. Mus. 



Horizons. — Sabine ?, St. Maurice and Claiborne Eocene. 



Localities. — Claiborne, Ala. ; Orangeburg District, S. C. ; 

 Centre Hill, ? S. C. 



Glycymeris lisbonensis, n. sp., PI. 20. Figs. 12-15. 



General form, size and characteristics as shown by the figures. 

 A thinner, more nearly circular shell than either staminea or 

 idonea, with more sharply pointed beak ; and, posses.sing when 

 young comparatively strong concentric lines, while the radiating 



