8 PHYLOGENY OF FUSUS AND ITS ALLIES. 



type species, the Mtirex coins of Liniie. Later authors have generally 

 tended to greater restriction of the genus, by elimination of non-char- 

 acteristic species, though some have attempted to extend again the 

 meaning of the term. 



In all the characterization of the genus, the form has been consid- 

 ered as of paramount importance. While it is true that no species 

 which have not a true fusoid form can be relegated to this genus, it 

 is also true that numerous species have a fusoid form which are not 

 genetically related to Fusiis, and hence can not be placed in that genus. 

 The only true guide to relationship in this as in all cases, must be found 

 in the development of the individual, i. c, its ontogeny, and its relation 

 to that of the members of its group, i. e., its phyletic relation. For this 

 purpose the earliest whorls and particularly the protoconch are of the 

 greatest import, and no species which does not show a protoconch sim- 

 ilar to that of Fusus colus, the type of the genus, can be relegated to 

 Fusus. On the other hand, there are species of gastropods (Hemifiisiis, 

 Rhopalithes, etc.) which have a Fusus protoconch, thus evidencing an 

 unmistakable relationship to Fusus, but their form forbids that they 

 be included under this genus. Thus the genus becomes still more 

 restricted, and very many, perhaps most, of the species which Lamarck 

 and some subsequent authors included in it must be removed to other 

 genera. 



The Protoconch of Fusus. 



The protoconch of Fusus is distinctive, and has been observed in 

 the following twenty-one recent and Tertiary species : 



F. porrectiis, F. colus, F. novcc-hoUandia , 



F. aciculatus, F. tuberculatus, F . longirostris, 



F. acuminatns, F. distans, F. marmoratus, 



F. aspcr, F. clostcr, F. hrasilicnsis, 



F. henekeni, F. dupetit-thouarsii, F. rostratus, 



F. eucosmius, F. irregularis, F. hredcc, 



F. turriculus, F. ambustiis, F. carinatus. 



The protoconch is seldom preserved in recent shells. This is 

 chiefly due to carelessness of collectors, who do not protect the apices 

 of the shells properly, and to the deplorable habit which many col- 

 lectors have of treating their shells with acids, thus destroying the 

 finer characters of the apex. In spite of this unfavorable condition 

 of most collections, the protoconch has been seen in so many individuals 

 of the above-named species that no doubt exists in my mind of its 

 relative constancy of form and characters. 



The protoconch generally consists of one and a half volutions, but 

 may be somewhat shorter or longer. No case has been observed in 

 which the protoconch consists of zs few as one volution, and only one 



