PARALLELISM AND CONVERGENCE 



977 



is probably derived from a Pleurotoma-like ancestor, and not a 

 true Fusus at all.* (Fig. 252.) 



The Eocenic genus Clavilithes furnishes a number of striking 

 examples of this similar development or homoeogenesis, as Eimer 

 has termed it.f (Fig. 260.) 



The typical species of this genus, C. parisiensis, from the Cal- 

 caire Grossier of the Paris Basin, finds its almost exact equivalent 

 in the modern Cyrtulus serotinus, Hinds, of the Marquesas region 

 in the South Pacific. Clavilithes became extinct in the Eocenic. 

 while Cyrtulus is a derivative from the modern stock of Fusus. 

 But by far the most interesting type of this complex series is 



Fig. 260. Clavilithoid shells showing "convergence." a, b. Cyrtulus sero- 

 tinus. A modern clavilithoid, being the phylogerontic terminal of 

 the Fusus series (slightly reduced), c. The protoconch and 

 early conch stages of Clainlithcs parisiensis, an Old World 

 Eocenic clavilithoid (enlarged), d. Clavilithes {?) kcnnedy- 

 anus, a New World Eocenic clavilithoid of independent origin 

 (slightly reduced). 



Clavilithes scalaris (Lamarck), from the Sables Moyens of France. 

 This species is characterized by a projecting rim or flange on 

 the shoulder of the adult whorl. This same feature is reproduced 

 in Clavilithes longccvus (Solander) of the Barton Beds of England, 

 which is of wholly independent origin. Again, Clavilithes ? cham- 

 berlaini, Johnson and Grabau, from the Lower Claibornian of 

 Texas, shows the same type of structure, and here, too it is inde- 

 pendently derived. Finally, Rhopalithes japcti (Tournouer) repre- 

 sents this same feature in a genus entirely distinct from Clavilithes 



* The distinction is not accepted by all. (Grabau-14.) 



t The controversy regarding this and the other species mentioned here is 

 dealt with by Grabau {i2,:622 et seq.) in the Studies of Gastropoda III. 



