268 
DEVONIAN FAUNA. 
Bemarhs. — These specimens are easily distinguished by their peculiar form. 
They are all sinistral, and the flatness of the whorls increases with the growth of 
the shell, so as to give a peculiar unsymmetrical appearance to the spire. The speci- 
mens in the Museum of Practical Geology are rather more elongate than the others, 
and their whorls are somewhat more convex, but they clearly belong to the same 
species. 
The narrow band, which truncates the otherwise sharp keel of the back, has 
much the appearance of a sinus-band, and as such I was at first inclined to regard 
it. In this case it would of course belong to the genus Pl&urotomaria. But in no 
instance does it show any signs of a flexion of the growth-lines, and I now 
think that in all probability it does not indicate a labial sinus. In some specimens 
I cannot detect this band, and it seems replaced by a simple rounded edge. 
Affinities. — From Trochus petrseos, Miinster,^ these fossils differ in size, in being 
sinistral, in having decidedly narrower whorls, and in having fewer (twelve instead 
of fifteen) spiral threads, and more prominent transverse threads, so that the 
surface is more definitely reticulate. Trochus Neptuni, Miinster,^ is another closely 
allied dextral shell, differing in being much more elevated, in having a beaded 
spiral ridge immediately below the suture, and in having fewer spiral threads. It 
is, however, reticulate like the English form, which thus comes midway between 
these two German shells, but is distinguished from both by being sinistral. The 
latter character is constant in the English specimens, and with the other differ- 
ences is ample to constitute a specific distinction. 
Sandberger regards Miinster's Trochus petraeos as belonging to a section of 
Pleurotomaria which he calls Nodulosae, and defines as sinistral and granuliferous. 
PI. elegans, d'Arch. and de Vern.,* which is figured by Goldfuss,* and is the 
same as PI. nodulosa, Sandberger,^ but not as PI. antitorquata, Phillips (not 
Miinster), approaches very near to this species, which is distinguished from it 
by its flatter, more pagoda-like shape, its reticulate rather than granular ornament, 
its size, its more angular whorls, and especially by the acute ridge or angle imme- 
diately above the band ; these features bring it nearer to PI. exiliens,^ which again 
differs in the perfect flatness of its whorls and its granular ornament. From 
these shells, however, the absence of a sinus-band seems definitely to separate it. 
There is nothing which could at all represent it in Phillips's ' Pal. Foss.' Mr. 
Vicary's specimens were labelled by Salter " left-handed species, distinct from 
1 1840, Miinster, ' Beitr.,' pt. 3, p. 88, pi. xv, fig. 16. 
2 Ibid., p. 88, pi. XV, fig. 15. 
2 1842, d'Archiac and de Verneuil, ' Greol. Trans.,' ser. 2, vol. vi, pt. 2, p. 360, pi. xxxiii, figs. 3, 3o — c. 
* 1844, Groldfuss, ' Petref. Grerm.,' vol. iii, p. 63, pi. clxxxii, fig. 10. 
^ 1853, Sandberger, 'Verst. Ehein. Nassau,' p. 200, pi. xxiv, figs. 13, 13 a— c; and 1842, 
G. Sandberger, in ' Neues Jahrb. f. Min.,' p. 390, pi. viii b, fig. 4. 
^ 1853, Sandberger, ' Verst. Ehein. Nassau,' p. 200, pi. xxiv, figs. 12, 12 a. 
