34 PHYLOGENY OF FUSUS AND ITS ALLIES. 



individuals of this variety have a portion of the last whorl without ribs 

 or keel, being thus comparable to F. coins. 



In typical specimens of this variety from Japan (Nat. Mus. 

 125894a, 123734a) the angularity of the whorls appears slowly, on the 

 rounded regularly ribbed whorls of the early neanic stage. For about 

 three whorls the angulation and ribs prevail together, after which, 

 in the metephebic stage, the ribs disappear, while the keel still retains 

 its strongly noduled character. Finally, in the parephebic stage, the 

 nodules disappear, the keel remaining simple thereafter. This is the 

 coins stage, and it js followed in one specimen by the early gerontic 

 stage, in which the keel disappears too, leaving part of the last whorl 

 uniformly convex (longicaudus stage). A specimen from Yokahama 

 (Nat. Mus. 36554) nearly five inches in length, retains the nodulated 

 keel to the end, though the ribs disappear in the last whorl. The 

 shoulder of the adult portion of the shell is flat, and strongly delimited 

 by the tuberculated keel. This is the most primitive (unaccelerated) 

 individual of the species observed, and for the present series (that of 

 F. perplexus) it represents what F. tubcrculatns and F. torcitmus repre- 

 sent for their respective series. 



In the young of this and a number of other specimens a marked 

 bicarinate aspect is imparted to the whorls by the strengthening of a 

 spiral below the central one, which is itself strengthened. In one of 

 these specimens this double carination is continued on later whorls after 

 the appearance of the angulation. This feature appears to be true also 

 of Lischke's typical specimens. 



Connecting Lischke's with Adam's typical form are a number of 

 intermediate forms, showing various degrees of acceleration. In some 

 cases the angular ribbed whorls pass abruptly into angular whorls 

 without ribs or nodes, a simple keel remaining. This passes into a 

 keelless stage. In other specimens nodes or tubercles continue for 

 a time, on the angular but ribless whorls, the whole merging grad- 

 ually into a ribless, tubercleless and keelless round-whorled stage, 

 where even the primary spiral is indistinguishable. 



In all these specimens intercalated spirals appear early in the 



round-whorled stage. 



The Typical Form. 



(Fusus inconstans, var. Lischke.) 

 The essential characteristics of Adams' species are : " . . . 

 anfractibus 7, convexis, longitudinaliter obsolete plicatis, transversim 

 liratis, liris acutis aequalibus undulatis, lineis elevatis filiformibus alter- 

 nantibus, liris transversis subnodulosis in medio anfractuum instructis." 

 This is the variety which Lischke has named var. minor (I, pi. II, figs. 

 3-6). This "variety" falls again into several "subvarieties," which 

 are comparable to the various species in the latter part of the colus 



I 



