GRAMMOCERAS FLUITANS. 191 



Discoidal, compressed, carinate. Whorls in shape subquadrangular, ornamented 

 with coarse, rounded, ventrally-projected, arcuate ribs which sometimes coalesce 

 near the inner margin to form a slight protuberance. Ventral area rather broad, 

 slightly gibbous, carrying a small but distinct solid carina. Inner margin well 

 defined, quite smooth, almost upinght. Inclusion not quite one half. Umbilicus 

 scored with coarse, irregular ribs. 



This species is the descendant of Gramm. toarcense — of one of the forms which 

 have ribs joined occasionally near the inner margin (p. 172). Its development 

 from such a form has followed the normal course (p. 134). It is distinguished 

 from Gramm. toarcense by its flatter, broader whorls, smaller umbilicus, more 

 acute ventral area, and more prominent carina ; from its " cousin," Gramm. 

 doerntense, by its more compressed and more involute form, its coarser ribs, and 

 more prominent carina. Its i"elation to Gramm. aalense is that of parent, and it is 

 therefore very similar to that species, but differs, as would be expected, in being 

 thicker, more umblicate, and coarser-ribbed. 



Dumortier's figure of this species represents a specimen larger than I possess. 

 Branco's figure seems to be a variety of this species with less conspicuous, but 

 more distant ribs. 



This very scarce species occurs in the Opalinum-zone (Moorei-heds) at 

 Haresfield and Frocester Hills. 



PI. XXX, figs. 1, 2, give two views of a very good little specimen of this 

 species. 



GrRAMMOoBRAs, sp. Plate XXXII, figs. 11, 12. 



1886. Haepoceras fltjitans, Vaceh. Oolithe Cap saii Vigilio; Abb. d. k.-k. geol. 



Keicbsaustalt, Wien, Bd. xii, No. 3, 

 pi. ix, Hg. 6. 



Vacek's figure represents a form which differs from Grammoceras Jiuitans in 

 being considerably more compressed ; and in this respect it is to a certain extent 

 intermediate between that species and Gramm. aalense. It, however, differs from 

 the latter by the absence of united ribs in the inner whorls. The specimen which 

 I have had depicted seems to agree very well with Vacek's figure ; but as it pos- 

 sesses no centre I cannot say much about it. 



This specimen came from the Opalinum-zone {Moorei-hed&) of Haresfield Hill. 

 Its more regular, more distant ribs separate it from the specimens referred to 

 Gramm. aalense. 



PI. XXXII, figs. 11, 12, represent two views of this specimen. 



