Nigerian Eocene Mollusca. 17 



Semiterebellum elongatum, sp. nov. 



PLATE 2, figs. 14, 15. 







DESCRIPTION. Shell elongate, subulate, depresso-convex ; spire narrow, 

 composed of about ten longitudinally deep volutions obliquely sutured, including 

 about 3j smooth apical whorls, with an obtuse nucleus ; body-whorl cylindrical, 

 considerably taller than the penultimate, nearly parallel-sided ; aperture forming 

 a trigono-oval cavity, widely emarginate at the base, narrow posteriorly where it 

 terminates on the suture with a recurved canal ; labrum thickly margined, 

 slightly excavated in the centre, but rounded, and enveloping, at the base ; 

 columella excavated, covered with a moderately wide callosity ; ornamentation 

 consists of spiral striations crossed by numerous oblique, rather obscure costa- 

 tions, the earlier whorls of the spire furnished posteriorly with a minute marginal 

 collar consisting of two or three spiral lines bearing small tubercles, from which 

 descend the more or less feeble longitudinal costae, an obscure carination exists 

 in well preserved specimens a short distance above the suture. 



DIMENSIONS. 



Alt = 42 millimetres. 



Lat - 10 



REMARKS. This shell is related to the new form of Semiterebellum which 

 I have named suturocostatum, having a similarly structured posterior canal. 

 It is more elongate, however, and has no denticle on the labrum, the suture is 

 thin and not ornamented with vertical costae, although the earlier whorls are 

 minutely, narrowly, and spirally banded at the suture, besides being furnished 

 with tubercles of microscopical size, from which emanate a series of obscure 

 longitudinal costations. An obtuse spiral carination is evident about a millimetre 

 above the suture, a structure similarly represented in the type of this genus 

 Rostellaria marceauxi of Deshayes, from the older Eocene of Europe, further 

 ornamentation being also in partial agreement with that observed in the figure of 

 the type. According to M. Cossmann Semiterebellum is intermediate between 

 Rostellaria and Terebellum, and is limited to Paleocene and Eocene rocks 

 (Paleoconchologie Compared, 1904, part 6, pp. 27, 28). 



OCCURRENCE. Cuttings Nos. 5, 6, 10, 12, 14, 15. 

 COLLECTOR. Mr. Kitson. 



