PHYLOGENY OF FUSUS AND ITS ALLIES. 53 



The middle spiral (the ii()per of the two) finally becomes the strong 

 central carina. The spirals on the body of the whorl are stronger 

 than those on the shoulder. 



The shoulder gradually becomes concave, and the ribs on it become 

 gradually suppressed. They continue, however, on the shoulder angle, 

 where they form strong but blunt and rounded nodules. Intercalated 

 spirals appear on the shoulders in the third whorl. 



A number of young shells in this stage have been found, but no 

 adult shell of this series has been seen in which the development ceased 

 at this point. If such were found, as may not be improbable, it would 

 constitute the torcumiis type of this series. 



The next stage in the development of this species, is the coins 

 stage, characterized by the loss of the ribs, as well as the nodules on the 

 periphery. The shoulder, however, remains concave and no strong 

 single spiral occurs, but rather several which produce a somewhat un- 

 defined angulation. 



Figures 2 and 3 of plate VI represent this species in its typical form. 

 In figure 2 the last whorl and a half are ribless, the shoulder is concave 

 and the body of the whorls marked by strong spirals. This is slightlv 

 more accelerated than Brocchi's type, in which the ribs continue onto 

 the last whorl. Figure 3 shows a specimen which is somewhat more 

 accelerated than the preceding, and may be considered as representing 

 the toreumoides type of this series. It has two ribless whorls, in the 

 last of which the concavity of the shoulder is less marked. The 

 toremnus stage is faint, though still visible. 



Young specimens of this species which have been obtained from 

 the Vienna Basin appear to be less accelerated than those from Italy. 

 The round whorls continue longer and the ribbed and noduled whorls 

 are more pronounced. It may be that the more primitive toreumiis type 

 occurs in the Vienna Basin. The specimens figured by Homes from 

 that district (pi. 32, figs. 6, 7) are more primitive than the majority 

 seen from the Italian localities. The ribs persist to the end and the 

 shoulder is only faintly concave, there being only a moderate peripheral 

 angulation. 



The specimen illustrated in Hcn-nes' fig. 5. nuist be referred to F. 

 castchnqiiatcnsis, though the early whorls show a faint peripheral 

 angulation which is not found in the typical specimen. 



A young specimen of this species from Bordighera, Italy (M. 

 C. Z. 27797), shows a less degree of acceleration than is found in 

 most individuals. The protoconch is slightly depressed, and con- 

 sists of something over one and a half volutions. The last portion 

 has smooth vertical riblcts, rather far apart and without indications of 

 spirals. The protoconch terminates in a varix. 



