PLEUROTOMARIA. 
279 
8ize. — Height 17 mm., width about 18 mm. 
Localities. — There are three rather poor specimens in Mr. Vicary's Collection, 
and two small indistinct specimens in the Museum of Practical Geology, 
from Wolborough. In the Bristol Museum is a small specimen from Lum- 
maton. 
BemarJcs. — These specimens are all imperfect, and are so much weathered that 
no finer ornamentation can be seen. Hence they do not in themselves show any 
distinctive marks of the genus Pleurotomaria. However, they so closely resemble 
PI. subclathrata as described and figured by Sandberger, that Mr. Roberts 
and I came to the conclusion that they must be regarded as undoubtedly 
belonging to that species, the only difference being that the English shells are 
rather more coarsely ornamented than are Sandberger's types. On the other 
hand, they are so similar to various species of the genus Gydonema of HalP that 
it would be necessary to refer them to it, were it not that the fine ornamentation 
shown in Sandberger's figure proves that his shell is certainly a species of 
Pleurotomaria. 
Turbo nanus, Eichwald, is either the young of this species or of Trochus Ivanii, 
Lev. It seems somewhat more elongate than the former, but exactly agrees with 
it in ornament, and I am therefore disposed to regard it as identical. 
Affinities. — Trochus Yvanii, Leveille,^ as shown by the original figure, is more 
elongate, and has finer, more numerous, and equal spiral lines. It appears to 
have an umbilicus, and is certainly distinct from the present species. It is a 
Carboniferous shell. As figured by Goldfuss,^ it is a more globose shell, with 
many more spiral ridges, than the English species. Again, as given by 
de Koninck from the Carboniferous of Belgium, under the name Pleurotomaria 
Yvanii, Lev.,* it is sometimes as little elevated, but seems to differ in having all 
the ridges equal and similar, except those of the base, which are closer. In 
de Koninck's later work, where he calls it Baylea Ivanii, Lev.,^ it exactly 
corresponds with Leveille's original type. 
None of the other species which de Koninck refers to his genus Baylea, 
which seems synonymous with Hall's Cyclonema, approach our English shell 
more nearly. 
D'Archiac and de Yerneuil give a Devonian variety of Trochus Ivanii,^ which 
1 1879, Hall, ' Pal. N. T.,' vol. v, pt. 2, p. 34. 
2 1835, Leveille, 'Mem. Soc. Geol. Fr.,' vol. ii, p, 39, pi. ii, fig. 24. 
^ 1844, Goldfuss, ' Petref. G-erm.,' vol. iii, p. 51, pi. clxxviii, fig. 9. 
* 1842-4, de Koninck, 'Desc. Anim. Eoss.,' p. 390, pi. xxxvii, figs. 1 a — c and 7 a — e. 
5 1883, de Koninck, ' Ann. Mus. Eoy. H. N. Belg.,' vol. viii, pt. 4, p. 69, pi. xxvii, figs. 1—5, and 
pi. xxxii bis, figs. 8, 9. 
^ 1842, d'Archiac and de Yerneuil, ' Geol. Trans.,' ser. 2, vol. vi, pt. 2, p. 359, pi. xxxii, fig. 16. 
