niYLOGENY OF FUSUS AND ITS ALLIES. 6l 



very strongly marked. In this stage the shoulder in the typical speci- 

 mens is flattened and the spirals on it are numerous, fine and closely 

 crowded. 



Gerontism is marked in this species, as in the preceding, In' a return 

 of the whorl to the rounded, round-ribbed, primitive condition with 

 the outer lip drawn into a strong rounded fold and the inner lip separated 

 from the columella. 



A very large shell apparently closely related to this species was 

 figured by Homes (pi. 32, fig. i) as a variety of F. rostratus. In this 

 the asperations on the periphery are very strong, and the shoulder 

 is moderately convex. There are about two and a half volutions more 

 than in fig. 3, pi. VII, which resembles it. The specimen, with another, 

 was found in the lower Tegel of Baden in the Vienna Basin, a forma- 

 tion considered of Miocene age. This species was afterwards separated 

 by Hoernes and Auinger as Fttsus aiistriacus. 



Localities: Italy, Castelarquato ; Asti in Piemonte (M. C. Z. 1452- 

 1455, 27806) ; Baldissera, Grangia (Bellardi). 



Horizon: Pliocene Subapennine formation, Etage 27. Also re- 

 corded from ]\Iioccne med. (Bellardi). 



FUSUS SEMIRUGOSUS Bellardi and Michelotti. 



(Plate VIII, figs. 9-12.) 



1840. Fnsiis scminigosus Bellardi et Michelotti, Saggio Orittografico, p. 13, 



tav. I, fig. 13. 

 1856. Fusus semiriigosus Hornes, Foss. Moll. Tert. Beck. Wien, p. 294. pi. 32, 

 figs. 8-10 (with bibliography). 



This is an advanced species of the rostratus stock, in which through 

 loss of ribs in later whorls, a phylogerontic stage of development has 

 been reached. It represents the terminal member of a lateral branch 

 from F. rostratus. 



The protoconch is fusoid, consisting of one and one half volutions 

 ending in a prominent varix, and ornamented in the last half volution 

 by fine closely set vertical riblets, which in some specimens are only 

 seen with difficulty. The whorls of the conch are rounded with 

 rounded vertical ribs, separated by concave interspaces of about equal 

 width. The spirals, which appear suddenly after the end of the proto- 

 conch, are sharp, subequally distant and decrease gently in thickness 

 towards the sutures. The interspaces are wider than the spirals. 

 Intercalated spirals appear in the fourth volution of the conch. .\ 

 slight angularity with a faint flattening of the shoulder appears in some 

 of the later whorls, there being some variation in the age of the indi- 

 vidual when these appear. A faint concavity occurs just below the 

 suture, delimiting a su])sutural band, which becomes quite prominent in 

 the later whirls and indicates the presence of a posterior canal through- 



