PLEUROTOMA (HEMIPLEUROTOMA) GASTALDII. 209 



Pleurotoma (Hemipleurotoma) plebeia (Sowerby). Plate XXVI, figs. 9, 10. 



1850. Pleiirotoma j)lebeia, Sowerby, in Dixon's Geol. Sussex, p. 184, pi. vi, fig. 23. 



1856. Pleurotoma plebeia, Forbes, Tert. Fluv-mar. Form., Isle of Wight (Mem. Geol. Survey), p. 154, 



pi. V, fig. 1. 

 1861. Pleurotoma denticula, F. E. Edwards, Mon. Moll. Eoc. Form. Eugl. (Palffiont. Soc), p. 286, 



pi. XXX, fig. 7. 

 1891. Pleurotoma {Hemipleurotoma) plebeia, Harris and Burrows, Eoc. Olig. Paris Basin (Geol. 



Assoc), p. 98. 

 1896. Pleurotoma {Hemipleurotoma) plebeia, Cossmann, Ess. Palooconcli. comp., vol, ii, p. 78. 



Specific Characters. — Shell small, turreted, elongato-conical, sub-cylindrical ; 

 whorls 7 or 8, the upper ones finely striated, with a rather prominent tuber- 

 culate keel, slightly concave above it, decussated by the lines of growth, the 

 lower part of the body-whorl excavated and ornamented by strong spiral ridges ; 

 suture well-marked, channelled, with a thickened line on both sides of it ; apex 

 obtuse ; mouth oval, angulate above ; canal narrow, short, nearly straight. 



Dimensions. — L. 13 — 25 mm. B. 5 — 7 mm. (Of Crag specimens) — L. 9 mm. 

 B. 3 — 5 mm. 



Dlstrihntlon. — Not known living. 



Fossil: Waltonian Crag: Little Oakley (derivative). British 

 Eocene : London Clay, Barton and Bracklesham beds. Paris basin ; Middle and 

 Upper Eocene. 



BemarJcs. — The smaller of the two specimens figured under the present name 

 (PI. XXVI, fig. 9) was found at Oakley. In general appearance and colour 

 it differs essentially from the Crag shells, agreeing with one in my collection from 

 the Barton beds of Hampshire, and is, no doubt, an Eocene derivative. 



It was referred by Edwards in 1861 {op. cit.) to P. denticula, a characteristic 

 and abundant shell of the Miocene of Bordeaux, described above, but this is 

 generally considered to have been a mistake, recent writers reverting to the name 

 P. plebeia, originally proposed for it by Sowerby. The latter is an Eocene form, 

 the former, as just stated, a Miocene species. 



Pleurotoma (Hemipleurotoma) Gastaldii (Bellardi). Plate XXVI, fig. 19. 



1847. Pleurotoma Oastaldii, Bellardi, Mem. R. Accad. Sci. Torino [2], vol. ix, p. 572, pi. ii, fig. 8. 

 1877. Pleurotoma Gastaldii, Bellardi, Moll. Terr. Terz. Piem., pt. ii, p. 50, pi. ii, fig. 8. 



Specifi.c Characters. — Shell subfusiform ; spire elongate ; apex acute ; whorls 

 nearly flat, generally without ornament, the last half the total length ; suture 

 slight ; mouth ovate, ending in a short, straight and narrow canal. 



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