PIIVLOC.KNY OF FUSUS AND ITS ALLIES. II3 



1069, 1072, 27752, 1078, II 18; 27725, 27755, 27756; Auvers (M. C. Z. 

 1093) ; Loins (M. C. Z. 27758). 



Horizon: Eocene (Middle; Deshayes). Calcaire grossier. 



CLAVILITHES TUBERCULOSUS (Deshayes). 



(Plate X, fig. 4.) 

 1837. Fttstis tiihcrculosus Deshayes, Coq. Foss. Env. Paris, t. 2, p. 522, pi. 7;^. 



figs. 14, 15. 

 1889. ClavilitJics tubcrculosus Cossmann, Cat. Coq. Foss., p. 174. 



The shell here illustrated, thotigh iminature, appears to be a distinct 

 species derived from C. daiiicriaccusis. T have identified it with 

 Deshayes' Fitsiis tubcrculosus, which, as far as description and illustra- 

 tion allow us to judge, has the characters found in the shell under con- 

 sideration. The early stages are like those of C. daincriaccnsis, the 

 rugosus stage being represented by a number of ribbed whorls and the 

 dameriaccnsis stage by spirally striate rounded whorl.s. Toward the 

 end of the latter, however, the sutural shelf characteristic of C. 

 parisicnsis is developed, without the change from a rounded to a 

 cylindrical form of whorl. This association of dauieriaccnsis and 

 conjunctus type of whorl with parisicnsis shelf appears to be character- 

 istic of this species and indicates an unequal acceleration, where a feature 

 characteristic of a late stage in one series is added to those character- 

 istic of an earlier stage in the same series. Tn other words, one feature 

 is accelerated while the others are correspondingly retarded in develop- 

 ment. The subsutural concavity characteristic of C. conjunctus is 

 strongly developed in this species, and to this is due the rotund char- 

 acter of the whorl, which is ordinarily lost with the development of 

 the sutural shelf. This shelf is an independent development in this 

 species. 



The ribs of the rugosus stage of this species are usually much 

 stronger than those of the corresponding stage of C. dameriaccnsis, and 

 give the characteristic tuberculous appearance at the suture. Since 

 the specimens which I have seen are all immature it is impossible to be 

 certain that they do not represent the young of the next species (C. 

 subscalaris) . As will be shown later, C. subscalaris passes through 

 a stage (neanic) which is the structural equivalent of the adult 

 (ephebic) stage of C. tubcrculosus. 



A specimen from the middle Eocene of Parnes (Acad. Sci. ) which 

 has been identified by Cossmann with this species has more the char- 

 acters of an excessively thick-set and short-spired C. rugosus. The 

 whorls are bulging, and the ribs are far apart and swollen in the middle. 

 They become obsolete toward the sutures, below which there is a strong 

 concavity. On the last whorl the ribs are fainter, and the concavity 



