DRILLIA SIGMOIDBA. 225 



RemarJts. — The Oakley fossil figured under the above name, although differing 

 materially from the form I have taken as typical of D. incrassata, seems to belong- 

 to the same group. It is less delicate than the type, with much coarser sculpture, 

 differing from the varieties dertomagna and crassa, in which the longitudinal costse 

 are more numerous, less prominent, and generally confined to the upper whorls, 

 while the spire is slender and elongate. It approaches very nearly the shell 

 described by Nyst as Pleurotoma incrassata, with which I propose to associate it, 

 dedicating it to that distinguished scientist as a variety of what was evidently in 

 Pliocene times a very variable form. Like the latter they have the deep and 

 rounded labial sinus with the pad on the inner lip characteristic of this species, 

 which unfortunately, in the present case, the artist has not clearly shown. 



Drillia sigmoidea (Bronn). Plate XXVII, figs. 24, 25. 



1831. Pleurotoma sigmoidea, Brouu, It;il. Tert. Geb., p. 47. 



1847. Bapliitoma sigmoidea, Bellavdi, Mem. E. Accad. Sci. Torino [2], vol. ix, p. 637, pi. iv, fig. 29. 



1853. Pleurotoma Suessi, Homes, Foss. Moll. Tert. Wien, vol. i, p. 384, pi. xl, fig. 13. 



1875. Conopleura sigmoidea, Seguenza, Boll. R. Com. Geol. Italia, vol. vi, p. 206, no. 172. 



1877. Drillia sigmoidea, Bellardi, Moll. Terr. Tert. Piem., pt. ii, p. 144, pi. v, fig. 4. 



1890. Brillia sigmoidea, Sacco, Boll. Soc. Geol. Ital., vol. ix, p. 273, uo. 4091. 



8'pecijic Characters. — Shell turreted; whorls strongly convex, tapering to a fine 

 point, longitudinally costate, costse prominent, sigmoid, separated by wide furrows, 

 hardly reaching the base of the shell ; suture deep ; mouth wide, with a short 

 canal ; labial notch large, with a pad on the inner lip as in D. incrassata ; base 

 striated. 



Dimensions. — L. 12 — 14 mm. B. 4 — 5 mm. 



Distribution. — Not known living. 



Fossil : Waltonian Crag : Little Oakley. Newbournian : Xew- 

 bourn. 



Miocene : Italy (Tortoniano), Vienna basin. Lower Pliocene : Italy — Ligurian 

 coast, Castelnuovod'Asti. Upper Pliocene: Biot, Bologna, Li vorno; Sicily — Altavilla. 



Bemarhs. — I have two or three specimens from Oakley which correspond more 

 or less nearly with some of the present species which I brought from the Italian 

 Pliocene of Albenga. They are rather worn, but not too much so for identifica- 

 tion. The Messrs. Ogden, however, have recently found another, perfect and fresh, 

 at Newbourn, which is here figured. This form may be recognised by its convex 

 whorls, its deep suture and sigmoid costee ; it is allied to D. incrassaia, but both 

 Bellardi and Prof. Sacco consider it a separate species. It has rather an extended 

 range in time, from the Miocene of Italy and the Vienna basin to the Upper 

 Pliocene of Sicily and the English Crag. I see no reason for considering it 

 derivative in the latter. 



29 



