PHYLOGENY OF FUSUS AND ITS ALLIES. 



a slight hollow in the upper whorl of some specimens, as if a partial 

 volution had been broken away. The smooth whorls are followed 

 by whorls with narrow sharp riblets, which are close together on the 

 upper part of the whorl, but separate towards the center until they are 

 from two to four times their width apart, and then approach each 

 other again towards the umbilical side of the whorl, their lower ends 

 being hidden by the succeeding whorl. This type of riblets con- 

 tinues for about a third or a half volution, after which the riblets be- 

 come concave forward, on the upper part of the volution and convex 

 forward on the lower portion. The outline is something like a reversed 

 letter S. The general slope of the riblets is downward and forward. 

 After the completion of the first ribbed volution the riblets become 

 more crowded, but the interspaces are of irregular width. Fine spiral 

 lines make their appearance between the ribs, where 

 they are hardly visible even with a magnifier. 

 After the completion of over one and a half ribbed 

 volutions of the protoconch the riblets merge into 

 the ribs of the conch, there being no definite varix. 

 Towards the end the ribs are vertical and subequally 

 spaced. There appears to be a very fine barely 

 visible spiral sculpture on the ribbed portion of the 

 protoconch, traces of which have been seen through- 

 out. 



The conch begins with whorls which almost 

 from the outset show an angularity. This is due 

 to the strengthening of the three central spirals, 

 the middle one being strongest, while the lower one 

 is covered by the edge of the succeeding whorl. The 

 shoulder is flat and even gently concave, and has one 

 spiral near the center and another just below the 

 suture. The passage appears to be direct from protoconch to angu- 

 lated whorl. 



Not until the beginning of the fourth volution or sometimes much 

 later is there any intercalation of spirals, and then only on the shoulder 

 next to the suture band. Later, another spiral appears between this 

 last one and the suture band. Intercalation also occurs between the 

 lower of the three primary spirals and the spiral next below, but it 

 is rarely observed on other parts of the shell. Very faint revolving 

 lines may, however, be seen between most of the spirals. 



The inner lip is not commonly developed to any extent except in 

 adult individuals. On it is shown the influence of the spirals, pro- 

 ducing pseudo-plications. There are also short horizontal plications 

 which make a considerable angle with the former. 



The general characters of the species have been so well described 

 by Dall that they need not be given here. A remarkable specimen 



Fig. II. Heil- 

 prinia caloosaen- 

 sis. (After Dall.) 



