I06 PHYLOGENY OF FUSUS AND ITS ALLIES. 



spirals sometimes appear, occurring at times even in pre-ephebic stages. 

 The shoulder is somewhat flattened, and near the suture becomes 

 slightly concave. The lines of growth are not infrequently strong and 

 imbricating, strongly cancellating the spirals, which are sometimes 

 nodose at the intersection. 



Gerontic characteristics are shown by the 

 separation of the inner lip from the columella, 

 and the consequent formation of an umbilicus 

 (pi. IX, fig. 3). Also by the disappearance of 

 the ribs and the excessive development of the 

 posterior canal. 



An elongated variety of this species is figured 



in fig. 8, plate IX. In this the whorls are loosely 



coiled, appearing more rounded ; the ribs are more 



pronounced throughout, and secondary spirals 



Fig. 15. Clavilithes are well developed. This latter feature marks 



rugosus, the proto- j-|-jjg variety as more accelerated in development in 



'^^ ' ' this respect, than the normal species. 



Localities: Paris Basin (M. C. Z. 1380, 1373, 1377 var., 1378) ; 



Grignon (M. C. Z. 1374, 1379, 1375)- Var. M. C. Z. 1413, Young M, 



C. Z. 1 125. 



Hori::on: Calcaire Grossier ; Eocene. 



CLAVILITHES DAMERIACENSIS (Deshayes). 



(Plate X, figs. 5 to 8; Plate XI, fig. 6.) 

 1866. Fustis dameriacensis Deshayes, Anim. sans vert., T. 3, p. 256, pi. 85, figs. 



23, 24. 



The protoconch of this species is of the normal papillose type, of a 

 little more than three volutions, umbilicated and with septa. The last 

 portion is furnished with fine vertical riblets which are smooth, but 

 have fine thread-like spirals in the interspaces. This merges into the 

 normal whorls of the conch. 



The conch is ribbed and spirally striate from the beginning, the 

 whorls changing from the cvlindrical form of the protoconch to a 

 rounded one. They embrace up to the middle of the preceding whorl, 

 thus making the ribbed spire less elongate. This is the chief difference 

 between the young of this species and C. rugosus. The ribs, at first 

 strong and widely distant and uniform throughout, increase in strength 

 on the periphery but become obsolete towards the sutures. In the 

 fourth or fifth volution the ribs disappear altogether, while at the same 

 time intercalated spirals appear between the primary ones. The spirals 

 are uniform and equidistant except near the suture, where they are 

 more crowded. The last whorl or two of the conch are ribless, rounded 

 and covered with more or less strongly marked spirals, which become 



