l8 PHYLOGENY OF FUSUS AND ITS ALLIES. 



advance in development, due to acceleration in the evolution of the 

 Parisian over the British individuals. The ribs of the whorls are 

 narrow, accentuated, but rounded on top, and separated by interspaces 

 which are several times as wide as the ribs. The spirals are strong 

 and sharp, producing a series of asperations on the ribs which recall 

 F. asper, but are less marked than in that species. The carinate as- 

 pect of the whorl is about as strongly marked as in the British 

 species. Three spirals are characteristic of the shoulder. The space 

 between the spirals of the body whorl and those of the spindle is 

 generally furnished with an intercalated spiral in the later whorls. 

 These intercalated spirals appear early in some specimens and not 

 until the last whorl in others, showing different degrees of accelera- 

 tion. 



In the larger specimens the ribs often become obsolete on the 

 last whorl and the carina is also suppressed. These features are 

 gerontic, and not individual, but mark a general decadence of this 

 branch of the genus. Normally this variety shows a distinct advance 

 over the English variety, as it is characterized by the accentuation and 

 earlier appearance of all the progressive features of the species, which 

 in the British variety appeared late in the ontogeny and were never 

 strongly developed. On the other hand, further advance through 

 continued accentuation of the progressive features appears to have been 

 prevented by the peculiar conditions which existed in the Paris Basin ; 

 and in common with other species of the family, F. aciculatus assumed 

 gerontic characteristics. 



Localities: Paris (M. C. Z. 1411, 1412) ; Panics (M. C. Z. 

 1410). 



Horizon: Eocene, Calcaire Grossier of the Paris Basin. 



This species appears to be a local modification of the variety char- 

 acterizing the British Eocene. While we must thus postulate a con- 

 nection between the British and the French Eocene Basins, permitting 

 species to migrate from one to the other, the individual characters of 

 the species in the two areas show that the connection was not such as 

 to allow free intercommunication. 



2. THE FUSUS COLUS SERIES. 



This series comprises the typical Fusi, including the type species, 

 Fusiis coins Lamarck. The species of this series are characterized by 

 the possession of a long slender spire and a similarly slender and 

 elongated spindle. Fusiis coins occupies a somewhat advanced posi- 

 tion in the series, possessing some of the features characteristic of the 

 terminal members of the series. This group of Fusi has its earliest 

 representation in the Miocene ( ?) of the Antillean region, but no 



