PHYLOGENY OF FUSUS AND ITS ALLIES. 



43 



set ribs and marked by both primary and secondary spirals. This stage 

 rather more resembles the F. reevcanus type of whorl than that of F. 

 turriciihis. The angularity of the succeeding whorls is less accentuated 

 in this variety, though the longissiniiis stage is well developed. After 

 this stage the nodes become weaker, the ribs at the same time becoming 

 obsolete. A flat or very gently convex shoulder remains, bordered by 

 a keel free from tubercles. 



This is probably an accelerated individual in which the iindatiis 

 stage has been mostly replaced by a keel. On the other hand, it may 

 be a case of premature senescence. 



Localities: Pacific Islands (Nat. Mus. 36564, B. S. 220) ; Ceylon 

 (M. C. Z. 882) ; East Indies (B. S. 223) ; Taheiti (Acad. Sci.). 



The close relation between the preceding two species and F . tnhcr- 

 culaUis is shown by the slender spire, which often recurs in the former 

 species. The spire is that of F. tnhcrculatus, and it is particularly well 

 reproduced in the Academy of Sciences' specimen of F. tindatns Gmel. 

 The relation is also show^n in the nndatus tubercles which sometimes 

 appear on specimens of F. tubcrculatus (see above). The spire of 

 the specimens of the present series is not always nor perhaps even gen- 

 erally as slender as that of F. tiiherculatns, and for that reason, as well 

 as for the reason that F. longissimns is nearer in form and size to F. 

 nodosoplicatiis, it is best to regard the species of the present series as 

 derived from F. nodosoplicatiis rather than from F. tiiherculatns direct. 

 The relations may be expressed as follows : 



F. nndatus. 



F. nodosoplicatiis lischkii. 



I 



F. perplexus. 



F. longissitnus. 



F. distans var. 



F. perplexus nagasakii. F. distaits.- 



-F. nodosoplicatus. 



F. tiiberculatus. 



< 



F. closter. 



F. distans. 



W 



6. THE FUSUS BECKII SERIES. 



This series is to be traced directly to F. tiiherculatns, the features of 

 which are preserved in the early whorls of the species of this series. 



FUSUS BECKII Reeve. 

 1847. Fusus heckii Reeve, Iconica, sp. 34, 34a {F. vcntiicosus Beck, Mss.). 



The only specimen of this species which has come imder my ob- 

 servation is in the collection of the Philadelphia Academy of Sciences. 



