Il6 PHYLOGENY OF FUSUS AND ITS ALLIES, 



In fig. 6 the ribs are very faint, but otherwise the specimen is like 

 the preceding except that in the last portion of the last whorl the shelf 

 projects slightly outward as in C. scalaris. This occurs before the 

 disappearance of the spirals which are simple, or with intercalations 

 only in the upper part of the whorl. In fig. lo is shown a young speci- 

 men in the tuhcrculosns stage, the shelf appearing at about the 

 time of the disappearance of the spirals. In fig. ii is shown a 

 specimen in which the shelf is faintly marked in the ribbed stage, 

 though perhaps scarcely sufficiently to be considered a rugoso-tuber- 

 culosus stage. The sitbtubercnlosus stage is very short, having been 

 practically eliminated. The tubcrculosns stage occupies about half a 

 volution, and is followed by the parisicnsis stage. In figs, i, lo and ii 

 the ribbed whorls (rngosus stage) are unusually persistent. 



Fig. 9, the type of the species, is a strongly accelerated individual 

 of the Clarilithes series. The shelf appears in the fourth whorl before 

 the ribs have disappeared {ntgoso-titbcrculosiis stage) and rapidly be- 

 comes prominent. The spirals disappear with the ribs, thus cutting 

 out the sitbtubercnlosus stage. The tubcrculosns stage continues for 

 about half a volution or more, and then merges into the parisicnsis 

 stage. The shelf becomes very prominent and begins to project beyond 

 the shell below, thus faintly approaching the characters of the scalaris 

 stage. This stage, however, does not occur. 



Fig. 12 shows a differently accelerated individual. The rugosus 

 stage is short and faintly ribbed, the shelf not being formed until the 

 disappearance of the ribs. A short subtubercnlosiis and longer tuber- 

 cnlosus stage occurs, and then the parisicnsis stage becomes strongly 

 developed. This, therefore, is a typical C. siibscalaris only with the 

 earlier stages differently accelerated than in fig. 9. 



A specimen from Loins, France (M. C. Z. 27754), is extremely 

 accelerated. There are two and a half normal rugosus whorls, then a 

 subsutural thickening occurs, which soon develops into a shelf. This 

 though narrow is pronounced. There are nearly two volutions which 

 have ribs and a shelf, the latter even projecting slightly after the 

 scalaris manner. The spirals disappear half a volution or more before 

 the ribs, the latter gradually passing into undulations. Shortly after 

 the disappearance of the ribs the whorls become cylindrical and the 

 shelf is no longer rimmed. 



Localities: Paris (M. C. Z. 1077, Bronn ; 1071, Lyell ; 1102, Duval, 

 1070; 27748, Duval; 27757, Dyer) ; Cuise-Lamotte (M. C. Z. 27749) ; 

 Chamery (27744; 27745 Type; 27769 young?); Nanteuil (M. C. Z. 

 1074, Reneault) ; near Nantes (M. C. Z. 27751); Panics (M. C. Z. 

 27742) ; Chaumont (M. C. Z. 27747) ; Loins (M. C. Z. 27754, Dyer). 



Horizon: Middle Eocene, Calcaire Grossier. 



