152 DEVONIAN FAUNA. 



identical with Sp. Uneata, Martin, sp., but left the question undecided. Under 

 Sp. Uneata he included as varieties Sp. elliptica, Phillips, 1 and Sp. imbricata, 

 Sowerby, 2 sp., but afterwards separated the latter on account of the different shape 

 of its spirals. An examination of a large series of Carboniferous specimens of 

 the above shells shows that in them the fold and sinus are generally absent, are 

 very rarely clearly marked, and never deflect the transverse ridges. Waagen 

 concludes from Davidson's description that dental plates are absent, though they 

 are certainly mentioned by M'Coy. 3 



Our Pilton specimens are with two exceptions much distorted, and none show 

 the ornament except under the aspect of a mould. They all have definite signs of 

 a fold and sinus, which frequently deflect the transverse strige ; their transverse 

 ridges are few and coarse, being not more than fifteen or twenty ; their spines are 

 just visible to the naked eye. One cast shows short but evident arching dental 

 plates. In another the spines are seen to be bicanaliculate (as described by 

 Davidson in a Carboniferous shell). Those specimens which seem to be least 

 distorted are slightly transverse, and the curvature of the front margins some- 

 what approaches a semicircle. Hence it appears that they constitute a form which 

 does not seem to vary much, and which differs considerably from the general run 

 of Carboniferous forms, but most nearly approaches Sp. imbricata. Whether the 

 difference should be regarded as of specific or only varietal value remains yet to be 

 decided ; but if Sji. imbricata be distinct from Sp. Uneata, the presumption is 

 that the present form is equally distinguishable from each of them, and therefore 

 it seems preferable to resume, at least provisionally, Phillips's specific name. 



2. Spirifeka Vernetjilii, Murchison. Plate XVIII, figs. 9 — 13 a. 



1840. Spirifer Verneuili, Murchison. Bull. Soc. Geol. Pi\, vol. xi, p. 252, 



pi. ii, figs. 3 a — e. 

 1840. — Lonsdalii, Murchison. Ibid., p. 251, pi. ii, figs. 2 a — c. 



1840. — Archtaci, Murchison. Ibid., p. 252, pi. ii, figs. 4 a — c. 



185S. — — Pacht. Baer aud Helmeren's Beitr. Euss. Eeiches, 



Band xxi, p. 95. 

 1864. Spirifera disjuncta, Davidson. Brit. Foss. Brach., vol. iii, p. 23, pi. v, 



figs. 1 — 12 ; and pi. vi, figs. 1 — 5. 

 1868. Spirifer disjunctus, Dames. Zeitsch. Deutsch. Geol. (resell., vol. xx, 



p. 494. 



1 1836, Phillips, ' Geol. Yorks.,' pt. 2, p. 219, pi. x, fig. 16. 



2 1822, Sowerby, ' Min. Concb.,' vol. iv, pi. cccxxxiv, fig. 3. 



3 1855, M'Coy, < Brit. Pal. Poss.,' p. 429. 



