64 PHYLOGENY OF FUSUS AND ITS ALLIES. 



becomes pronounced and vertically flattened as in the most advanced 

 Pliocene species. The shoulder, however, never loses its convexity 

 as it does in the fossil species, though it may become considerably de- 

 pressed (fig. 21 ). Occasionally the ribs become obsolescent in the last 

 portion of the body whorl. The more accelerated individuals ap- 

 proach F. ccelatus Reeve (Iconica, pi. 8, figs. 35 a-b), which appears 

 to be a variety of this series in which the spirals and ribs are both 

 strongly developed, producing a striking appearance. 



Locality: Mediterranean (M. C. Z. 923, 924, 925). 



Habitat: 20 to 100 fathoms on corals and rocks (Tryon). 



In the collection of the Academy of Natural Sciences in Philadelphia 

 are a number of specimens labelled Fitsits rostratns var. carinata. The 

 specimens are from Greece and represent the most accelerated recent 

 types of the series yet seen. 



The protoconch is of the normal Fitsiis type with numerous crowded 

 vertical riblets on the final portion and ending abruptly with a varix. 



The conch begins with round whorls furnished with broad round 

 ribs which are crossed by strong revolving lines of which five are usually 

 visible above the suture, the fifth being often covered in part by the 

 succeeding whorl. In the third volution, the central spiral develops 

 into a prominent carina, the shoulder at the same time becoming flat- 

 tened. The ribs also become more widely separated until they are 

 about twice their width apart or more. They also become obsolete 

 on the upper portion of the shoulder. Intercalation begins with the 

 appearance of the angulation. The central carina attains almost the 

 sharpness of that of the milder varieties of F. brcdce as shown in fig. 

 I of pi. VII. The flattened shoulder and the prominent intercalations 

 make the resemblance in some cases very marked. 



It is a remarkable fact that the Pliocene varieties appear on the 

 whole to be more accelerated than the recent ones. The flattening of 

 the shoulder is rare in the recent varieties, nor have any specimens 

 been seen in which the keel is as strong and sharp as that of F. bredcu. 

 Furthermore, gerontic types like F. semirugosus are not as yet known 

 in the recent fauna, though common in the Tertiary. If it is proved 

 to be a fact that the Tertiary species are more specialized than the 

 modern ones, for the determination of which large collections of 

 recent and Tertiary specimens from all parts of the Mediterranean 

 region are required, the explanation may be found in the independent 

 development of the Tertiary series in a circumscribed provincial area. 

 The highly specialized species are, so far as I am aware, recorded only 

 from the Piedmont district, and the suggestion presents itself that the 

 separation may have been due to the influence of the forming Apen- 

 nine chain. 



