STROPHEODONTA. 153 
chief arguments in favour of this are the great difference in size and the absence 
of specimens of intermediate dimensions, and also the fact that the variations in 
its ornament are not, on the whole, in such a direction as to make it probable that, 
if a specimen were assumed to grow to the size that L. nobilis constantly reaches, 
its ornament would, in that case, be at all similar. 
Another species which is not always easy to distinguish from it is Stropheodonta 
nodulosa, Phillips, sp.; for, while the two shells are typically very different, some 
flattish specimens with fine major ribs are not very dissimilar. 
The shell which Waldschmidt refers to St. corrugatella belongs clearly, I think, 
to this species, and it seems to me not impossible that the Llandeilo St. corruga- 
tella, Davidson, may itself prove specifically identical. 
Billings’ figure of the American St. varistriata seems identical with the English 
shell, but Hall’s figures are not quite so like. I should think that it was probably 
only a local variety. Billings remarks that it perfectly agrees with St. inequt- 
radiata‘ except in size. The latter shell, however, is distinguished from the 
present by having very much more numerous ribs. 
Strophomena interstrialis, Barrois,? seems a much larger, longer, and flatter 
shell, so that I doubt its identity with the present species, and think that it agrees 
with St. teniolata, Sandberger.® 
Whiteaves regards it as certainly belonging to the sub-genus Stropheodonta. I 
had independently come to the same conclusion. 
4. StRopHEODONTA ? NOBILIS, M‘Coy, sp. 
1852. Leprena nopiuis, M‘Coy. Brit. Pal. Foss., p. 386, pl. ii, fig. 8. 
1865. — (?) — Davidson. Brit. Foss. Brach., vol. ili, pt. 6, p. 86, pl- 
xviii, figs. 19—21. 
1882. —_ _- Davidson. Ibid., vol. v, pt. 1, p. 53. 
2? 1882. SrropHomeNa NOBILIS? Barrois. Mém. Soc. Géol. Nord, vol. ii, p. 242. 
- Localities—From Lummaton there are thirteen specimens in my Collection. 
From Wolborough there are three specimens in Mr. Vicary’s Collection, and three 
in the British Museum. 
Remarks.—As remarked by Davidson, this species is very closely allied to 
Stropheodonta interstrialis. The chief distinctions are the very great difference 
1 1867, Hall, ‘ Pal. N. Y.,’ vol. iv, p. 87, pl. xi. figs. 2481; pl. sii, fig. 12; and pl. xiii, figs. 6—11. 
2 1882, Barrois, ‘Mém. Soc. Géol. Nord,’ vol. ii, p. 248, pl. ix, figs. 8a, 6; and 1889, ibid., vol. iii, 
p- 64, pl. iv, fig. 8. 
8 1854, Sandberger, ‘ Verst. Rhein. Nassau,’ p. 360, pl. xxxiv, figs. 11 a—d. 
VoL. Il. 20 
