PIIYLOGEXV OF FUSUS AND ITS ALLIES. IO3 



This species occurs with the others of this genus at Cuise in the 

 Paris Basin. It is commonly classed a^ a variety of Clavilithes 

 parisicnsis Mayer (=^^ C dcformis (Sol.) Cossmann or C. longceviis 

 (Lamarck) of Deshayes and other authors). 



Localities: Cuise (M. C. Z. 1097, 27730) ; Comprigne (M. C. Z. 

 27740). 



Horizon: Lower Eocene. 



Young specimens of this generic series can not generally be placed 

 in the species to which they belong, since all the species have in young 

 stages the characters of more primitive species of the series and assume 

 their true specific characters only in the adult stage. Thus fig. 16 is 

 in the ribbed stage, resembling the most primitive type of the series, of 

 which, however, no representative has been found (unless the Eocene 

 species of Fusits be considered such). Certainly if an adult specimen 

 with the characters of fig. 16 were found, it would have to be placed near 

 the true Fusi, since the protoconch and other characteristics of such a 

 species would approach those of that genus. The ribs of the early 

 whorls of Clavellofusiis are more widely spaced than is the case with 

 any species of Fusits I have seen, but this feature may occur in shells 

 which otherwise conform to the characteristics of that genus. This 

 stage then is the Fusus stage of the ClaveUoftisiis series, just as the 

 young of CyrHilns represents the Fusus stage of that series, and clearly 

 indicates the ancestry of that genus. In the Clavilithes series, this 

 stage is represented by C. rugosus, and is there known as the rugosus 

 stage. (For further discussion see beyond p. 105.) 



In like manner it will be seen that specimen fig. 18 is in the tuber- 

 culatns stage, being comparable to an adult C. tuberculatus of this 

 series, or an adult C. tubercitlosus of the Clavilithes series. It may 

 remain in this stage, simply increasing in size, or it may develop into a 

 C. spiratus by adding a cylindrical whorl. 



A constant and very characteristic feature of the species of this 

 genus is the sharp angle between the sutural shelf, and the side of the 

 whorl. This is particularly marked wdiere the whorls have assumed 

 the cylindrical habit of growth. The shelf generally slopes inward 

 and downward, rather than upward as in Clavilithes of the Paris Basin, 

 in which the angle is also more rounded. In this respect these shells 

 are similar to Clavilithes solanderi Grabau of the English Eocene, in 

 which the same type of shelf exists. The pointed apex and the small 

 size of these shells are also distinguishing features. 



Localities: The three species given above, together with inter- 

 mediate forms, and probably other species, occur together in the Lower 

 Eocene of the Paris Basin. 



Horizon: Lower Eocene, Sables inferieurs, Paris Basin (Deshayes). 



Synonymy: Fusus longccvus var. A. Deshayes, Coq. Foss. env. 



