PHYLOGENY OF FUSUS AND ITS ALLIES. 6/ 



ever, being covered up by the next succeeding whorl. Above these 

 central spirals on the shoulder are three other spirals, the third of 

 which is next to the upper margin of the whorl. The ribs are faint, 

 being more of the nature of undulations, broadly rounded and with 

 narrow concave interspaces. On the latter part of the third volution 

 an additional (fourth) spiral appears between the upper marginal one 

 and the one just below it. A little later intercalated spirals appear 

 between the three central primary spirals. 



With continued flattening of the shoulder the upper of the two ex- 

 posed central spirals becomes stronger, and projects above and beyond 

 the others as a strong keel. By intercalation and separation of sec- 

 ondary from primary spirals, the appearance of highly compound inter- 

 calation is produced. The lines of growth are strongly marked, pro- 

 ducing a vertical striation, which serrates the spirals. The ribs fade 

 away toward the sutures, being strongest and sharpest on the angle. 

 In some of the less accelerated specimens the whorls remain round 

 longer, the angularity scarcely becoming pronounced until the ephebic" 

 stage is reached. 



Accelerated individuals show a loss of angulation and tubercles in 

 the last whorl. One specimen (M. C. Z. 947a, PI. IV, fig. 4) has been 

 seen, in which the ribs are absent from the last two whorls, and the 

 angulation absent from the last whorl. This represents an advanced 

 coins type of this series (i. c, the coins variety of this species). It 

 almost approaches the lo)is;icandns type, which would be reached as soon 

 as the angular ribbed whorls are suppressed or replaced by rounded 

 ribbed whorls. In this, as in all the other series, whether they be 

 considered series of species (as would be most proper) or series of 

 varieties, or even subvarieties, the same order of variation prevails and 

 the same types of mutations (or more correctly the same types of 

 species) are reproduced. 



The color of the American specimens of this species is white, with 

 orange tipping on the tubercles. The coloration extends in a weak 

 stream downward and upward from the tubercle, biit soon dies out. 



A variety from ofif Cape Frio (M. C. Z. 961) shows a development 

 comparable to F. longissimiis. It represents the opposite extreme from 

 that shown in the longicmidns variety of this series (M. C. Z. 94/3.), 

 and represents a progressive rather than a retrogressive type. It agrees 

 with the normal form in the protoconch and early whorls, but the 

 shoulder becomes more concave, and the tubercles become vertically 

 flattened and strong. The spirals become faint to obsolete on the 

 shoulder. This variety has quite a distinct aspect, but it is clearly a 

 modification of the normal type. 



In some of the specimens of this series the ribs become bulging on 



