HELMINTHOCHITON. 
333 
length of the whorl, and smooth on the back, thus giving another point of distinc- 
tion from ours. 
BelleropJton Verneuillii, d'Orbigny,' is referred by de Koninck^ to Porcellia ; but,, 
as seen both from the descriptions by these authors and from specimens in the 
British Museum, it is a much narrower shell, and has only coarse radii on the 
inner half of the whorls, the outer half or back being quite smooth. It is a 
Carboniferous form. 
In Porcellia tuberculosa, Geinitz,^ as well as in Bellerophon tuherculatuSy 
d'Orbigny,* the longitudinal striee are replaced by rows of tubercles. 
Lastly the Carboniferous shell, to which Phillips incorrectly referred it, is easily 
distinguished by the very sharp angles on the shoulder and the margin of the 
umbilicus and by the coarse close granulation formed by impressed longitudinal and 
spiral strige. It was first described by Martin^ as Ammonites Woodivardii ; and its 
characters are distinctly shown by Sowerby^ who calls it Nautilus Woodwardii, by 
Phillips^ who calls it Bellerophon Woodioardii, and by de Koninck^ who calls it 
Porcellia Woodivardii, and are also very clearly displayed in several specimens in. 
the British Museum. 
Ckss— PLACOPHORA, Jhering, 1877. 
1. Orc^er— CHITONID^, D'Orhigny, 1837. 
1. Genus — Helminthochiton, Salter, 1847. 
This sub-genus of Chiton is thus defined by Salter :® "Elongate; plates as 
long as wide, subquadrate, thin ; apex of the anal plate remote from its front 
edge; sustentacula widely separated ; shell but very little covered by the mantle." 
1 1840, de Ferussac and d'Orbigny, ' Hist. Nat. Ceph.,' p. 212, (Bellerophon) pi. vi, figs. 12—14. 
2 1842-4, de Koninck, ' Descr. Anim. Fosa.,' p. 361, pi. xxviii, figs. 4 a, b. 
^ 1842, d'Arehiac and de Verneuil, ' Geol. Trans.,' ser. 2, vol. vi, pt. 2, p. 353, pi. xxviii, fig. 9. 
* 1852, Geinitz, ' Verst. Grauw. Sachsen,' p. 44, pi. xi, figs. 11, lla. 
^ 1809, Martin, ' Petrificata Derbiensia,' p. 17, pi. xxxv, figs. 4, 5. 
^ 1827, Sowerby, 'Min. Concb.,' vol. vi, p. 138, pi. dlxxi, fig. 3. 
7 1836, Phillips, ' Geol. Torks.,' vol. ii, p. 231, pi. xvii, figs. 1—3. 
^ 1842-4, de Koninck, ' Descr. Anim. Poss.,' p. 360, pi. xxviii, figs. 2 a — c. 
9 1847, Salter, ' Quart. Journ. Geol. Soc.,' vol. iii, p. 51. 
