Nigerian Eocene Mollusca. 13 



smoother although retaining a somewhat similar sculpture of closely set 

 spiral striations crossed by numerous longitudinal and more or less sinuous 

 lineations, the union of which produces a marked reticulation at the base ; 

 aperture narrow longitudinally and obliquely elliptical, widely notched at the base 

 followed by a straight, narrow canal ; labrum smooth within, furnished with a 

 thick reflected nearly perpendicular margin bearing 2 distant spinose digitations, 

 the lowest forming the posterior end of the notch ; columella smooth, obliquely 

 excavated, covered with a prominent enamelled callosity which becomes elevated 

 into a thickened tubercle posteriorly where it forms the lateral boundary to a 

 narrow canal in conjunction and parallel with the labrum. 



DIMENSIONS. 



mm. 

 Alt. ... ... ... ... .. ... ... = 80 (approximate) 



Lat. ... ... ... ... ... ... ... = 27 



REMARKS. This species, although distinguishable from previously described 

 forms of Rostellaria, may be compared with the well-known R. dentata, Grateloup, 1 

 from the older Miocene deposits of Europe. That shell, however, presents some 

 interesting distinctions, inasmuch as its spire is narrower, much less turriculate, 

 more elongately acuminate and provided with more depressed whorls united by a 

 lesser depth of suture, while the sutural margins are about on the same plane 

 throughout. The body-whorl is also more uniformly inflated. Further, the 

 prominent internal columella-tubercle, which is well in front of the posterior canal 

 is not present in the Nigerian shell, and moreover, the termination of that canal, 

 which touches the sutural margin of the penultimate whorl and the spreading 

 callosity extending slightly higher up the spire, together with the wide curvature 

 existing behind the posterior region of the labrum, are points considerably 

 differing from those in the present species, which shows that the termination of 

 the posterior canal is nearly parallel with the callosity-covering, and that both 

 exhibit only a diminutive curvature, their terminations rising slightly above the 

 sutural margin of the body-whorl. Sculpture details are very similar in both 

 species. With regard to the digitations of the labrum, only two are present in 

 the Nigerian shell, but on the authority of Grateloup a third one is occasionally 

 developed in the European form, R. dentata. The digitate growths are more 



1 Conchyliologie Tertiaires PAdour, 1840-1846 ; Vol. i Univalves, pi. i, figs, i, 2, 3, 4. 



