GYROCERAS. 97 



that faint indications of these growth -Hnes are visible in Phillips's type, though 

 they are too slight for delineation ; while on its dorsal side the distant thread-like 

 loops have entirely disappeared, and therefore his figure is quite incorrect in 

 showing them there. 



The small specimen of the apical termination, which I obtained from Lum- 

 maton, long caused me considerable perplexity, but a rather larger though more 

 decayed specimen in the Museum of Practical Geology from Wolborough proves 

 that it belongs to the present form, and that the section, which is at first circular, 

 becomes elliptic at a very short distance from the apical end. The rugged 

 growth-lines in this part are remarkable, as they seem to vanish, as we have seen, 

 in the median portions, and only to reappear when the shell becomes aged. I 

 cannot, however, from the paucity of the material before me, say how far this is a 

 general rule, or only the accidental character of a single specimen. 



As far as can be judged from our material the species does not seem very 

 variable, excepting that the ribs are not always accurately thirteen even in the 

 type-specimen. Thus the specific name is liable to criticism. 



Affinities. — C. acuticostatum, Sandberger,^ is so like the apical portion of this 

 species in its markings that in my earlier lists I referred the small Lummaton 

 specimen, above mentioned, to it. It seems, however, to taper less rapidly than 

 the present form. Very possibly it maybe the terminal coil of a Gijroceras instead 

 of a complete Cyrtoceras, and in that case may be identical with some unexpected 

 species. Gyroceras spinosum, Hall,^ has an almost circular section, and no longi- 

 tudinal ribs. Gyroceras cy clops, Hall,^ besides the difference in curvature, is 

 distinguished by having low, close, rounded, longitudinal folds in place of the 

 distant ribs which form so marked a feature of the English shell. 



5. Gyeoceras Eipelense, D^Arcliiac and de Verneuil, sp. PI. X, figs. 8, 9, 9 a, 9 h. 



? 1839. Cybtoceea. tentaculata, Munst. Beitr., pt. 1, p. 34, pi. ii, figs. 2 a — c. 

 1842. Cyetoceeas Eipelense, D'Arch. and de Vern. Geol. Trans., ser. 2, vol. vi, 



pt. 2, p. 349, pi. xxxi, figs. 2, 2 a, b. 

 1852 ? G-YEOCEEAS COSTATUM, Sandhergev. Verst. Ehein. Nassau, p. 136, pi. xii, 



figs. 5 a — d. 

 1853. LiTiriTEs Eieliensis, Steininger. Geogn. Beach. Eifel, p. 42. 



Description. — Shell flattened, much arched. Surface marked with thirty or 

 forty distant, rounded, longitudinal ribs, separated by interspaces which are 



' 1852 ? Sandberger, 'Verst. Rhein. Nassau,' p. 144, pi. xiii, figs. 5, 5a. 



2 1879, Hall, ' Pal. N. T.,' p. 382, pi. xlvii, fig. 8 ; pi. xlviii, figs. 1—5 ; pi. xlix, fig. 1 ; pi. xcviii, 

 figs. 1 — 7 ; and pi. xcix, figs. 1 — 8. 



3 Ibid., p. 287, pi. ci, fig. 1 ; pi. cii, fig. 1 ; pi. ciii, figs. 1, 2 ; and pi. civ, figs. 1, 2. 



