1 6 R. BULLEN NEWTON on 



canal short, posterior canal long, narrow and curved backwards on to the suture ; 

 labrum nearly vertical, unidigitate, thickly margined externally ; columella 

 evenly excavated, thickly callused posteriorly, the callosity curving backwards 

 to form the upper border of the posterior canal, then continuing as a smooth band 

 at the base of the whorls ; sculpture consisting of minute, smooth, spiral bands 

 divided by thin, microscopically punctuated furrows, as well as obscure longi- 

 tudinal growth striations. 



DIMENSIONS. 



Alt. 28 millimetres. 



Lat. ... ... 9 



REMARKS. This shell, numerously represented, is closely related in aper- 

 tural characters to R. unidigitata, and agrees in possessing one digitation on the 

 labrum. It differs, however, in being of a narrow, cylindro-conical shape, in 

 possessing a smooth spire, as well as a circlet of short rod-like costae covering 

 the sutural region. There is, likewise, no sutural platform, the whorls being 

 almost on the same plane, while the brephic volutions exhibit no longitudinal 

 costations as shown on the shell selected for comparison. Further features of 

 interest in this Gastropod include the backward extension of the narrow 

 posterior canal on to the margin of the costate, spiral collar, and the presence of a 

 wide callosity covering the base of the whorls of the spire, which, however, has 

 been sometimes obliterated by erosive agencies. 



This type of Rostellariform shell may be referred to Semiterebellum ot 

 Cossmann (Ann. Soc. R. Mai. Belgique, 1889, vol. 24, p. 91), which was 

 founded on R. marceauxi, Deshayes from the Lower Eocene of Europe. It is, 

 however, easily distinguishable from that species by the posterior canal being 

 reflected backwards, and resting more or less horizontally on the suture of the 

 body-whorl, whereas in R. marceauxi the corresponding canal extends up the 

 spire to within three or four whorls of the summit and in line with the margin of 

 the labrum. 



OCCURRENCE. Cuttings Nos. i, 5, 6, 10, 12, 13, 14, 15. 

 COLLECTOR. Mr. Kitson. 



