48 PHYLOGENY OF FUSUS AND ITS ALLIES. 



The stages of Fusus dnpetit-thoiiarsii may be summed up as follow : 



A. Protoconch. 

 Smooth. 

 Simple riblets. 

 Riblets and two spirals. 



B. Conch. 



1. Round whorled, round ribbed, non-carinate. 



2. Round whorled, round ribbed, bicarinate. 



3. Angular whorled, round ribbed, bicarinate. 



4. Angular whorled, ribless bicarinate-noduled. 



5. Angular whorled, ribless, unicarinate-noduled. 



6. Angular whorled, ribless, noduleless, unicarinately smooth- 



keeled. 



7. Round whorled, unicarinately smooth-keeled, 



8. Round whorled, keelless. 



When stages i to 5 occur together, the torcumns type is produced 

 (var. nodosus). When stages i to 6, or i to 7 occur together, the 

 coins type is produced (typical var.). Omitting stages 3 to 6 in- 

 clusive gives us the longicaiidus type (var. aplicatus), though this 

 variety may also be produced by developing stage 6, and even stage 

 3. Thus these so-called varieties vary again in a perfectly regular 

 and determinable manner. 



In its general aspect this shell is readily distinguished from other 

 species of the genus by its thick-set appearance, due to close coiling, 

 and by its proportionally short, slightly sinuous anterior canal. 



Localities: Pacific coast of America, Magdalina Bay (M. C. Z. 

 913) ; La Paz (M. C. Z. 912) ; Guaymas, West Coast Mexico (Nat. 

 Mus. 23677, 56338, 32335) ; Galapagos Islands (Nat. Mus., 48419, 

 dead shell) ; Puerto Libertad, Mexico (Nat. Mus. 152387) ; Carmen 

 Island (Nat. Mus. 32334) ; Cape St. Lucas (Nat. Mus. 13932, 5394) ; 

 Lower Cal. (Nat. Mus. 34512) ; no loc. (B. S. 221, M. Z. 911, 910, 909, 

 Nat. Mus. 36565, 56334) (Phil. Acad. Sci.). 



FUSUS DUPETIT THOUARSII var. IRREGULARIS var. nov. 



(Plate IV, figs. 5 and 6.) 



The protoconch of this species is of the normal Fiisiis type, though 

 appearing relatively larger. In all the specimens seen the apex was 

 bitten by acid, and so the details of the structure of the protoconch could 

 not be made out. Indications of the riblets have been observed, but 

 whether the spirals were present on the last part of the protoconch 

 could not be determined. It apparently ends in a varix. 



The conch begins with ribs which are to all appearances bicarinate 

 from the beginning. The whorls are otherwise round. The bicarina- 

 tion gradually gives way to a single carina, formed by the strength- 



