FHYLOGENY OF FUSUS AND ITS ALLIES. II7 



CLAVILITHES SCALARIS (Lamarck). 



(Plate X, figs. 2, 3; Plates XIII, figs. 13, 15-20.) 

 1816. Fiisits scalaris Lamarck, Encyclop. Meth. Tab., 425, fig. 7. 

 1822- Fiisus scalaris Lamarck, Anim. sans vert., t. VII, p. 134. 

 1837. Fusus scalaris Des haves, Coq. Foss. Env. Paris, t. 2, p. 525, pi. 72, figs. 



13, 14- 

 1866. FusHS scalaris Deshaves, Anim. sans vert., t. Ill, p- 257. 

 1889. Clavilithes longavus Cossmann, Cat. Coq. Foss., p. 172. 

 Not Miirex longcevus Solander, Brander's Foss. Hants., p. 22, pi. II, fig. 40, and 



pi. VI, fig. 72,- 1766. 



This species is the terminal member of the series as far as devel- 

 oped within the Parisian province. It is a highly accelerated type, 

 the ribbed riigosus stage being very short or dropped out altogether. 

 The sutural shelf begins early while the spirals are still strong on the 

 subtiiberciilosHS whorl. Not infrequently the shelf appears in the ribbed 

 whorls, forming a rugoso-tiiberculosus stage. In some specimens the 

 shelf appears as early as the third volution. A tubcrculosus and a 

 parisioisis stage normally follow the subtubercnlosus stage, but one or 

 both may be absent in highly accelerated varieties. The final stage of 

 this species — the scalaris stage — is brought about by the deepening 

 of the depression below the suture. The shelf as a consequence pro- 

 jects beyond the whorl as a rim. Coincidently the shoulder has become 

 very wide and is bordered by the swollen edge of the rim. The pos- 

 terior canal corresponding to this form of shelf has a T-shaped outline. 



There are several distinct varieties of this species. In the most 

 typical one (see Deshayes' figure) the shoulder appears after two or 

 three whorls of the conch and the ribs are almost obsolete. The pro- 

 jecting rim may appear while the shell is still in the tuberciilosus stage; 

 /'. c, round smooth-shelved whorls without spirals. Or it may appear 

 simultaneously with the appearance of the parisiensis stage ; i. e., when 

 the smooth-shelved whorl becomes cylindrical. The subtubcrcidosus 

 stage may be crowded out and the tubcrculosus stage follow directly 

 upon the ritgosus. Again, both subtiibcrciilosus and tuberciilosus 

 stages may be eliminated, and the parisiensis stage follow upon the 

 rugosiis stage. 



Numerous other variations are possible, and their characteristics 

 may be determined by permuting and combining the characters of the 

 various stages and substagcs in every manner possible. In a large 

 collection all or nearly all these possible variations may be found, since 

 hardly any two individuals are exactly alike. Except in the most 

 accelerated individuals a neanic C. scalaris and an ephebic C. stib- 

 scalaris are structurally equivalent, and every C. scalaris has the char- 

 acters of an adult C. subscalaris before it ac(juires those typical of its 

 own species. 



