PHYLOGENY OF FUSUS AND ITS ALLIES. 



143 



Fig. 22. Cosmo- 

 lithes uniplicatus. The 

 protoconch. ( M. C. 

 Z. 1127.) 



in the neanic and ephebic stages they are strong and stout in the 



middle, and fade toward the sutures. From the 



fact that about half of each whorl is covered by 



the succeeding whorl the ribs appear to be strong 



just above the suture and fade toward the upper 



portion of the whorl. 



Intercalated spirals appear in the second or 

 third volution of the conch. The columella is 

 furnished with one strong and one weak plica- 

 tion. 



This is the rugosus type of the present genetic series. It is char- 

 acterized by the strong sharp spirals, which are like those of Clavilithes 

 rugosus and the other "rugosus types" of the various genetic series 

 studied. The spirals are crowded and weak on the shoulder, but 

 strong and well spaced on the body of the whorl. The whorls em- 

 brace to near the middle, the shells thus assum- 

 ing a short depressed spire. The aperture passes 

 gradually into the canal, without the sudden con- 

 striction seen in Clavilithes rugosus. 



The erection of the protoconch and the 

 strengthening of the weak upper columellar pli- 

 cation produces Rhopalithes. In this connection 

 a specimen of R. rugoides in the collection of the 

 I^hiladelphia Academy is of interest (see above, 

 p. 136), showing a more intimate relation be- 

 tween the two types. 

 A plicated columella appears to indicate a more specialized develop- 

 ment than a non-plicate one. This is indicated by the fact that in the 

 young the plications are often weak, and where two plications exist in 

 the adult, the young sometimes show only a faint development of one, 

 while the other is strong. From this it seems not unlikely that 

 Rhopalithes is descended from Cosmolithes, and that the latter came 

 from some Fasciolarian ancestor. 



Localities: Grignon (M. C. Z. 1127) ; Paris (]\I. C. Z. 1133, 27770, 



Horizon: Eocene. 



COSMOLITHES SUBUNIPLICATUS sp. nov. 

 (Plate XIII, figs. 4-7.) 

 (Compare F. uniplicatus Desh.wes, Coq. Env. Paris, t. 2, pi. 94 bis, figs. 1-2.) 

 This species appears to be a derivative of C. uniplicatus, differing 

 from that species chiefly in the more pronounced characters of the ribs 

 which have more the form of strong undulations, but are more faintly 

 marked by spirals. The upper weak columellar plication character- 

 istic of the preceding species is also seen in some specimens of this 



Fig. 23. Cos m - 

 tithes uniplicatus. An- 

 other view of the pro- 

 toconch and young 

 shell stages. (M. C. 

 Z. 1127.) 



