150 PHYLOGENY OF FUSUS AND ITS ALLIES. 



transportation across the oceans, by the equatorial currents, would 

 seem an easy matter, and the world-wide distribution of the genus 

 within the equatorial belt would thus readily be accounted for. If, 

 on the other hand, the veliger stage should be passed through within 

 the egg-capsule as in Fidgur, or if, what seems not improbable in such 

 accelerated types as Fusus, the veliger stage is dropped out altogether 

 in the development, the problem of transoceanic migration by flotation 

 becomes a much more serious one. In that case we have to assume 

 that the egg-capsules, either separately or attached to sea-weeds, were 

 carried by the equatorial currents across the oceans, and become 

 stranded in favorable localities, where the young developed and ap- 

 propriated the territory. 



The development and migration of the Eocene Fusoid mollusks 

 of other genera {Falsifusus, Clavilithes, etc.) present problems ap- 

 parently as perplexing as that of the true Fusi. As has already been 

 shown, the American waters contained no true Fusi though species of 

 Fusoid form existed. Falsifusus may have been derived from a 

 Pleurotoma stock, from which stock also Levifusus appears to have 

 originated. Eiithriofusiis, the structural parallel of the latter genus, in 

 the Miocene of Europe, was perhaps derived from the Eocene Pseudo- 

 fusoids of the Paris basin. Fulgurofusus, the Eocene relative of 

 Fulgur, may have been derived from a Fasciolarian stock. From a 

 like stock, Heilprinia, was also derived, which during the Miocene 

 submergence of the isthmus, spread on both sides of the American 

 continents. Considerable doubt may be entertained as to the genetic 

 relation of Fnsus serratus Desh. and F. uniangularis Desh. of the 

 Parisian Eocene with the Pseudofusi of the Gulf state region. I am 

 strongly inclined to believe that their similarities indicate parallelism, 

 rather than relationship, and that they have arisen independently, and 

 so belong to distinct genera, a conclusion also suggested by their 

 structure. When we take into consideration the provincial character 

 of the faunas of which the Parisian species and the American Pseudo- 

 fusi respectively were members, it seems difficult to believe that any 

 communication could exist between the two regions. This suggestion 

 is not at all invalidated by the occurrence of Clavilithoids in both the 

 Parisian and the Gulf State Eocene, for, as has already been suggested, 

 it is not at all improbable that the two series have originated inde- 

 pendently, and that their striking similarities are merely pronounced 

 cases of parallelism. Cyrtulus serotinus, of the modern fauna, is 

 certainly as close to the Parisian Clavilithes in the characters of the 

 adult as the latter is to the American species referred to that genus. 

 Yet Cyrtulus serotinus, I believe, has no genetic connection whatever 

 with Clavilithes, being a phylogerontic Fusus, and clearly derived from 

 the modern members of that genus, while Clavilithes, though possibly 



