PHYLOGENY OF FUSUS AND ITS ALLIES. 1 37 



become prominent on the periphery while the shoulder is marked by 

 numerous fine uniform spirals, the primary ones being augmented by 

 intercalated secondary ones. On the body of the whorl the spirals 

 are coarse and distinct. The intercostal spaces become more and 

 more concave, giving' an undulatory instead of simply ribbed character 

 to the surface. 



In the nepionic stage this species has the character of neanic or 

 early ephebic R. rugoidcs, this being well shown in the young specimens 

 in figs. 14 and 15, pi. IX. Since the adult characters of R. rui:;oides 

 show a development in the direction of the R. no(U type, i. e., the sup- 

 pressing of ribs and angularity of whorl, it is evident that if R. 

 angulatiis is an ofTshoot from R. rugoidcs, its relationship is with the 

 more primitive varieties of that species. 



The gerontic stage of R. angiilatits has been seen in a few speci- 

 mens (M. C. Z. 1382, pi. IX, fig. 21), These are large for the species, 

 and the last whorl reaches up onto the preceding with the formation of 

 a strong posterior sinus. In the last part of the whorl the tubercles are 

 crowded and the strong asperations have become subdued. In another 

 specimen (M. C. Z. 1377) the last whorl has a rounded contour, the 

 angulation having disappeared. The ribs are rovmd and extend over 

 the entire surface as in a mature R. rugoidcs. The posterior canal is 

 deep and strongly marked, and the subsutural band is very prominent. 

 On the shoulder the spirals are fine, numerous and regular. On the 

 body they are coarse and distant. 



This individual is transitional to R. clavclloidcs, which is phylo- 

 gerontic. 



All the specimens examined, normal or accelerated, show two 

 strong oblique columellar plications. These are best seen on specimens 

 with broken outer lip, as they are only developed some distance back 

 of the aperture. In gerontic types they apparently become obsolete, 

 or at least are found only far back on the columella. 



Localities: Paris (M. C. Z. 1384, Baucoult, 1382, Koninck, 1377, 

 Duval) ; Grignon (1381, Agassiz, 1385, Duval, both M. C. Z.) ; Mont- 

 miraille (M. C Z. 1383). 



Horizon: Middle Eocene: Calcaire Gross. (Cossmann). Upper 

 Eocene: Sables Moyens (Desh.). 



RHOPALITHES CLAVELLOIDES sp. nov. 

 (Plate IX, fig. 22.) 

 1837. Fiisus angulatus van Deshayes, Coq. Foss. Env. Paris, t. 2, p. 521. pi. yi, 

 figs. 4, 5. 



This species holds the same relation to R. angulatus that R. nocc does 

 to R. rugoidcs. The last whorl is almost smooth, having lost its ribs, 

 which are only represented by faint undulations. The sutural shelf 



