PLEUROTOMARIA. 
303 
more elevated sinus-band, and by the greater flatness and peculiar slope of their 
whorls ; and after several examinations I have come to the conclusion that there 
is reason for treating them as a separate species. The sinus-band may possibly 
have been bounded by ridges, but the state of preservation of the specimens does 
not permit evidence upon this point. 
Affinities. — PI. naticiformis, Sandberger,^ exactly agrees with this species in 
shape, but is distinguished by its flat sinus-band which is divided into fine granules 
by three spiral furrows. 
PI. turhinea, Schnur,^ is distinguished by its numerous fine spiral strias and its 
more rounded and rapidly increasing whorls. 
PI. Ixvis, P. A. Romer,® differs in having much more numerous whorls, which 
increase more slowly and are less elliptic. He says it is the same species as that 
which he formerly described as Eu. Dionysii ? * and which chiefly differs from the 
present by having a higher spire and shallower sutures. Clarke^ says there is little 
variation in that species, and that the sculpture is so fine that it is often difl&cult 
to recognise the sinus-band. Hence it is probably distinct from the present shell 
in which the sinus-band is very clearly seen. 
I have named this specimen after the late Dr. Croker, of Bovey Tracy, an old 
student of the palaeontology of Devonshire. 
18. Pleueotomaeia geacilis, Phillips. PI. XXVIII, fig. 18. 
? 1840. Etjomphalus subcaeinatus, Miinster. Beitr., pt. 3, p. 85, pi. xv, fig. 5. 
1841. Pleubotomabia gracilis, Phillips. Pal. Foss., p. 98, pi. xxxvii, fig. 181. 
1854. — — Morris. Catal. Brit. Foss., p. 272. 
1888. — — Etheridge. Foss. Brit., vol. i. Pal., p. 164. 
Description. — Shell small, lenticular, much depressed, of about four volutions. 
Spire small, flatly conical. Suture narrow, linear, deep, simple. Whorls rather 
quickly increasing, rising from the suture and immediately curving with a 
decreasing curvature till the widest part of the whorl is reached, which is marked 
by the sinus-band, and immediately followed by the lower suture. Body-whorl 
rather large, similar to the other whorls above, and rapidly curving below to form 
' 1853, Sandberger, ' Verst. Ehein. Nassau,' p. 192, pi. xxiii, figs. 4, 4 a—c. 
2 1853, Steininger, ' Geogn. Bescreib. Eifel,' p. 47, pi. i, fig. 16; and 1853, Sandberger, 'Verst. 
Ehein. Nassau,' p. 192, pi. xxiii, figs. 5, 5 a — c. 
3 1850, F. A. Eomer, ' Beitr.,' pt. 1, p. 37, pi. v, fig. 27. 
4 1843, ibid., ' Verst. Harzgeb.,' p. 30, pi. viii, figs. 3 a, b. 
5 1884, Clarke, ' Neues Jahrb. f. Min.,' Beil.-Band iii, p. 340. 
