22 PHYLOGENY OF FUSUS AND ITS ALLIES. 



angulation. In such accelerated individuals the upper one of the three 

 central spirals increases in strength, and the space above produces the 

 flattened shoulder. The ribs become obsolete towards the sutures 

 but remain swollen on the periphery, thus giving the angulation a 

 resemblance to a subspinose carina. Such a subangulation is not in- 

 frequently followed by a return to a normal round-whorled condition, 

 when the ribs assume again their normal characteristics. 



Sometimes specimens occur which retain a more primitive form of 

 whorl and spiral, the latter remaining uniform throughout, though with 

 intercalations, while the whorls retain their rounded outline. Indi- 

 vidual senescence is marked by the obsolescence of the ribs of the last 

 whorl, and by the separation of the inner lip from the columella. 



The whorls of normal specimens of this species embrace only the 

 spindle of the whorl preceding, thus exposing as much of the whorl 

 above the lower as below the upper suture. This gives to the whorls 

 the appearance of resting the one upon the other, and gives the shell 

 a particularly graceful outline. In some aberrant individuals how- 

 ever {F. chinensis?) the whorls embrace more, giving the shell a 

 stouter aspect. This leads to such species as F. rccveanus Phill. 



Localities: China sea (M. C. Z. 915, 916, 917, 918, 33) ; China sea 

 (U. S. Nat. Mus. 18380-b, 91747) ; Manila, Stearns coll. (U. S. Nat. 

 Mus. 91748) ; China sea (Phil. Acad. Sci.). 



A magnificent specimen eight inches long, in the Haines collec- 

 tion of the American Museum of Natural History, shows the normal 

 gerontic characteristics of this species. The specimen is from the 

 China seas. 



About five normal volutions occur, with simple spirals and the 

 form and contour of whorls and ribs usual in this species. These are 

 followed by six volutions of the same type, but with additional spirals 

 intercalated between the primary ones. At the end of this, the 

 eleventh whorl, the size of the shell and all its characteristics are those 

 of the normal individuals of F. turriculus. The secondary spirals have 

 attained the size of the primary ones, and tertiary spirals make their 

 appearance. 



The last two whorls are free from ribs, except at the beginning, 

 where faint indications occur. The whorls are uniformly rounded, 

 and have all the characters of those of F. nobilis, to which this species 

 is a parallel. It is, however, much more slender than F. nobilis. It 

 will be observed that a larger number of young whorls are marked 

 with simple spirals than is the case in F. turriculus ordinarily. As far 

 as the early stages are concerned, then, this individual is more retarded 

 in development than the normal. The long life of the individual was 

 favorable to the development of normal regressive characteristics; no 

 indications of progressive characters, such as the incipient angulation 



