PHYLOGENY OF FUSUS AND ITS AI.LIES. 125 



Stage, as many as five volutions of this type having been noticed. They 

 simply increase in size and in the width of the sutnral shelf, but other- 

 wise they do not change. The shelf is abruptly marked off from the 

 whorl by a slightly acute angle, the shelf sloping inward. 



The whorls are not absolutely smooth, spiral lines appearing faintly 

 in the depression below the suture, as in C. conjiinctiis. In old-age 

 individuals, this depression becomes stronger, and a projection of the 

 sutural shelf is produced as in C. loiigccz'iis Sol. The shelf in this 

 stage also becomes somewhat more depressed, forming a modest 

 sutural canal. 



The increase in depth of the shallow depression below the shelf 

 resvilts in producing an outward bulge in the outer lip of the last whorl. 

 This gives a curvature to the lij), which in younger shells is perfectly 

 straight above. 



A gerontic individual of this species is figured by Sowcrby on 

 plate 63 of his Mineral Conchology. This has about six volutions with 

 a shelf, a little over five of which are of the normal type. The last, 

 however, shows old age characteristics in the development of a spinous 

 projecting rim of the Shelf. This character is normal to the adult of 

 the next species. The spinous prolongations are not true spines but 

 simply irregular extensions of the shelf with a depression below the 

 expansion. From the strong development of this depression the outline 

 of the whorl has again become rounded. The accompanying illustra- 

 tion (fig. 16) is a copy of Sowerby's figure. 



The distinctive characters of this species are produced by the ap- 

 pearance of the subconic shelved whorls immediately after the un- 

 dulating spirally striate whorls which represent the I'Kgosiis stage. The 

 species is in other words an excessively accelerated one, in which all 

 the smooth round-whorled stages are dropped out. In the subconic 

 form of the whorls this species is similar to C. macrospira Cossmann 

 of the Parisian Eocene, and it is not impossible that the two may prove 

 identical. The Parisian species is never so large and robust, and may 

 represent a migrant from the British province into the Parisian one. 

 From the difiference of physical condition it did not thrive well in the 

 Paris area, just as the migrant C. parisicnsis from the Paris province 

 did not thrive well in the British province, as indicated by the abnormal 

 development. 



Localities: Hampshire (M. C. Z. 1058, 1059) ; Barton cliff. Duval 

 (M. C. Z. 1061 and 1060) ; same, Keeping (27762). 



Horizon: Barton Beds. Upper Eocene. 



