98 PHYLOGENY OF FUSUS AND ITS ALLIES. 



The initial whorl, however, is not so swollen and elevated as is usual 

 in Fusus, but is rather depressed. In spite of this difference in the 

 initial whorl the final portion of the protoconch and the early whorls 

 of the conch are so typically of the Fnsiis type, that the derivation of 

 Cyrtuhis as represented by this species from Fiisus can not be doubted. 



It is to be noted that the ribs of the protoconch are more numerous 

 than in Fusiis, and are closely crowded. There is a suggestion of the 

 Falsifusus type of protoconch in the apical part, but the second whorl 

 is typically Fusoid. 



The conch is at first indistinguishable from a young Fusns of the 

 colus series. The whorls are round with rounded ribs separated by 

 interspaces of about their own width. After seven or eight whorls 

 of this type the turriculus stage comes to an end, being slowly replaced 

 by the toreumus stage. The shoulder angle it at first barely defined, 

 being indicated by the prominence of two central spirals. At this 

 stage intercalated spirals first appear. The shoulder angle gradually 

 becomes more distinctly defined, thus fully establishing the toreumus 

 stage. With this the spirals become less sharp, the ribs disappear and 

 the whorls become irregular, the later added portions reaching up onto 

 the earlier whorls. The angulation and the tubercles disappear, and 

 the spirals became more and more obsolete. The whorl becomes 

 smooth, thickened and enveloping. The posterior canal of the aperture, 

 always a gerontic feature, becomes strong and causes a shelf or flattened 

 shoulder on the upper portion of the whorl, next to the suture. The 

 spindle becomes more enveloped, and its form obliterated as the ephebic 

 whorls of this phylogerontic species are thickened. This results in the 

 production of a melongenoid form. The aperture becomes elongate as 

 in Pynila, Fiilgar, etc., and in extreme cases a tendency to uncoil and 

 form an umbilicus is shown. This melongenoid portion of the shell is 

 covered by a smooth brown periostracum. The preephebic whorls 

 show the coloration of Fusus. 



An old specimen (Nat. Mus. 130896) shows three whorls wrapped 

 around each other on about the same plane. 



Localities: Indo-Pacific (Nat. Mus. 130896, 91755, Dall) ; Pacific 

 Islands (B. S. 278, also Mayo coll.) ; Nonkahiva, Marquesas group, 

 S. Pacific (M. C. Z. 964, 963, Am. Mus. Nat. Hist., numerous speci- 

 mens). 



Habitat: In nine fathoms among sand. Hinds (Tryon). 



15. THE EOCENE CLAVILITHOIDS. 



Under this heading will be described the various species of Eocene 

 Fusoid shells which have assumed a melongenoid growth and are com- 

 parable to Cyrtuhis or Clavilithes, with which latter they are generally 

 classed. 



