50 PHYLOGENY OF FUSUS AND ITS ALLIES. 



are represented chiefly by nodules. These disappear also, and a 

 carinated stage remains. The carina slowly disappears, and the re- 

 maining whorls are round and marked only by strong spirals. 



FUSUS AMBUSTUS Gould. 



1853. Fusiis ambustus Gould, Bost. Journ. Nat. Hist., vol. VI, p. 385, pi. 14, 



fig. 18. 



The protoconch of this species is fusoid with narrow vertical ribs 

 on the last portion. No distinction is shown in the specimens seen 

 between the protoconch and the beginning of the conch, though in one 

 specimen there appears to be an indication of a varix. 



The conch appears to begin with three ribs which are slightly wider 

 than those of the protoconch, but are not like those of normal young 

 Fusus. It may be, however, that these ribs still belong to the proto- 

 conch, in which case the varix observed represents only a strengthened 

 rib of the protoconch. Between the ribs last mentioned as perhaps 

 belonging to the protoconch occur fine spirals, thus allying this species 

 very closely to F. dupetit-thouarsii. 



The whorls of the conch are at first rOund and the ribs uniform. 

 Then the central spiral becomes strong and, soon after, the spiral next 

 below becomes equally strong, thus producing a bicarination. The 

 spiral below the center does not quite reach the strength of the central 

 one, and the one above the center often becomes moderately strong, 

 thus producing an obscure tricarination. 



The largest specimen seen is nearly two inches long. The aperture 

 and anterior canal combined equal in length that of the spire. The 

 canal is slightly flexed. 



There is a certain resemblance between the young of this species 

 and that of F. dupetit-thouarsii. In the latter, however, the bicarinate 

 aspect is more strongly marked, while in F. ambustfis the bicarinate 

 aspect is faint, owing to the strengthening of the spiral next above the 

 center. Thus the angularity of the latter species is more normal, 

 the central spiral being strong, while those on either side progressively 

 decrease. 



In one specimen where the inner lip is well developed, six faint 

 columellar plications occur, which are disposed at a diflferent angle 

 from that of the spirals on the spindle, and not, therefore, produced 

 by them. The influence of the spirals on the lip is seen, however, in 

 the upper part of the aperture. In some of the other specimens faint 

 indications of columellar plications occur, which are situated too far 

 back to be due to the influence of the spirals. Similar faint plications 

 occur on the young of F. dupetit-thouarsii. 



Localities: West coast North America. Lower Cal., San Lucca 

 cove (Nat. Mus. 32344) ; Topolobampo (Nat. Mus. 150864) ; Mazat- 

 lan (Gould). 



