PHYLOGENY OF FUSUS AND ITS ALLIES. lO/ 



weaker, however toward the end. The subsvitural band and posterior 

 canal are well developed and characterize all the whorls from the 

 ncanic on. It is generally emphasized by a concavity which marks the 

 upper portion of all the later whorls, and is also faintly traceable on the 

 earliest ones. 



The characteristic features of this species are the strongly ribbed 

 vonng spire, in which there are from three to five volutions, and the 

 spirally striate ribless volutions of the adult. Both these features 

 show that this shell is still quite primitive when compared with the 

 other species of this series, in which the spire is scarcely ribbed, and the 

 last whorls are smooth and free from spirals. 



The rounded whorls without ribs, but with spirals, mark the 

 davicriaccnsis stage of the species of this scries. When present this 

 stage always follows the ribbed ritgosus stage. The present species, 

 C. dmncriaccnsis, consists of these two stages, the development of both 

 being about equal. 



Locality: Paris Basin (M. C. Z. 27750, 27724, 27775, -777^)- 



Horizon: Middle Eocene, Calcaire Grossicr (Desh.). 



CLAVILITHES CONJUNCTUS (Deshayes). 



(Plate X, fig. 6; Plate XI, figs. 1-5.) 

 1837. Fusus conjimctus Deshayes, Coq. Foss. Env. Paris, t. 2, p. 527, pi. 70, 



figs. 16, 17. 

 1889. Clavilithes conjuncttis Cossmann, Cat. Coq. Foss., p. 174. 



The protoconch of this species consists of from three to four volu- 

 tions, and has all the characteristics normal to this series. It merges 

 into the conch. 



The conch is spirally striate, the spirals being uniform and equidis- 

 tant. Towards the end of the first volution undulations appear, and 

 these in some specimens in the collection rise to the distinctness of 

 ribs. They are never very prominent, however, and after two or three 

 volutions they disappear again. Thus the ritgosus stage is condensed 

 in this species. This is followed by a short daincriaccnsis stage, in 

 which the ribless but round whorls are marked by strong spirals. 

 These spirals are strongest on the upper portion of the whorl, but 

 become faint and finally obsolete on the lower portion. Intercalated 

 spirals appear usually in the second or third volution of the conch, 

 though in some specimens they do not occur until considerably later. 



The whorls of the daincriaccnsis stage are succeeded by those of the 

 conjunctiis type. These, the final and typical w'horls of this species, 

 are still rounded but perfectly smooth or with the spirals so weak as 

 to be scarcely visible. This represents the next stage in advance of 

 the damcriaccnsis stage, and when well developed requires a condensa- 

 tion of the earlier stages to make roouL On typical specimens between 



