ORTHOCERAS. 141 



transverse ridges, about lialf the width of the intervening concavities. The whole 

 surface covered by very numerous, close, rounded, transverse strioB, about ten or 

 twelve times as numerous as the rings, and similar longitudinal striae by crossing 

 both rings and hollows, about half as numerous as the transverse strise, which thus 

 form a fine network over the shell. 



Size. — Section with diameters of 10 mm. and 9 mm. respectively. 



Locality. — One fragmentary specimen is in my Collection, from Lummaton. 

 Phillips's 0. ibex came from South Petherwin. 



Remarks. — My small specimen, though somewhat worn down by friction in a 

 quarry-boy's pocket, shows the markings very clearly. The outside test was 

 black and papyraceous, and probably, as the markings are clear upon the inner 

 coat, was, when unworn, very sharply ornamented. At first T supposed it to be a 

 specimen of 0. tuhicinella, Phil. ; but there are several reasons for separating it 

 from that species, e. g. its very oval section, its strong transverse striaB, and its 

 closer longitudinal strise. To the figure and description given by Phillips of his 

 0. ibex it comes very much nearer, being only separated by the presence of the 

 transverse strise, which are not mentioned by him, though he mentions the others. 

 I imagine, however, that it is the same shell as 0. ibex, Phillips, as the fact of 

 Phillips's identification would presuppose the existence of these striae. But from 

 the original 0. ibex, Sow.,^ as described by him and by Foord,^ the presence of 

 longitudinal striae most clearly distinguishes it. This distinction, moreover, is 

 further borne out by Blake,^ who distinguishes 0. ibex. Sow., as having only 

 transverse markings, from 0. tenuiammlatum, M'Coy,* which, as a specimen in the 

 British Museum shows, has fine thread-like strise quite distinct from the coarse 

 rounded rays of the present form. 



Affinities. — 0. Gerolsteinense, Steinihger,^ seems to be similar in its section, 

 and its septa have the same curvature as have the rings in 0. oryx, but as it is 

 only a cast it cannot be further compared. 



1 1839, Sowerby in March., ' Sil. Syst.,' p. 613, pi. v, fig. 30. 



2 1888, Foord, ' Cat. Foss. Ceph. Brit. Mus.,' pt. 1, p. 51. 



3 1882, Blake, ' Mon. Brit. Foss. Ceph.,' pt. 1, p. 98, pi. v, fig. 9. 



4 1851, M'Coy, ' Ann. Nat. Hist.,' ser. 2, vol. vii, p. 45 ; and 1832, M'Coy, ' Brit. Palaeozoic Foss.,' 

 p. 320, pi. xi, fig. 31. 



^ 1853, Steininger, ' Geogn. Besch. Eifel.,' p. 89, pi. viii, figs. 8 a, b, c. 



