114 PHYLOGENY OF FUSUS AND ITS ALLIES. 



is strong. There is no sutural shelf, and the spirals are strong. This 

 is probably an immature shell in which the shelf has not yet appeared. 

 The shelf is shown in Deshayes' figure of this species. 



Localities: Paris (M. C. Z. 1116, Koninck) ; Parnes (Acad. Sci. 

 6901, Cossmann, M. C. Z. 27760) ; Grignon (B, S. 1412). 



H orison: Middle Eocene, Calcaire Grossier. 



CLAVILITHES SUBSCALARIS sp. nov. 

 (Type Plate XII, fig. 9; var. Plate X, fig. i; Plate XII, figs. 1-3, 7, 8, 10-12.) 



This species is generally classed with C. parisicnsis to which it bears 

 a close resemblance in many respects, and especially to accelerated indi- 

 viduals of that species. It is, however, a much more accelerated species 

 and typical individuals are readily distinguished. The early stages 

 are generally much condensed, and the characteristic sutural shelf 

 appears in the early whorls, usually before the characteristics of the 

 early stages have disappeared. 



In the pre-ephebic stages this species has all the characters of C. 

 tiiherculosus, but it passes beyond that stage, assuming the cylindrical 

 shelved whorls characteristic of C. parisiensis with which it is identical 

 only in the ephebic stage. 



The diagnostic characters may be summed up as follows : Proto- 

 conch and earliest volutions normal. The ribbed stage occupies usually 

 a few whorls only. Succeeding ribless whorls are generally convex, 

 but soon merge into the cylindrical ones. The sutural shelf appears 

 with the disappearing of the ribs, sometimes earlier. It is strongly 

 developed, often projects outward to some extent, but does not form 

 the distinct rim of Clavilithes scalaris. Adult stage as in C. parisicnsis. 



The most prominent character of this species is the early appear- 

 ance of the sutural shelf which is also characteristic of C. scalaris. But 

 that species forms a projecting sutural rim or flange in the adult which 

 does not occur in C. subscalaris. There are many intermediate forms 

 which connect this species with C. parisicnsis, and hence some author- 

 ities consider them conspecific. It may, however, be emphasized that 

 similar gradations exist between practically all the species of the genus. 



The variations of this species are readily determinable from a con- 

 sideration of the various ways in which the stages can be combined. 

 By acceleration of one and retardation of another character, distinct 

 and important varieties are produced which form the connecting links be- 

 tween the primitive species on the one hand, and the highly progres- 

 sive on the other, thus showing an uninterrupted development gov- 

 erned according to the law of acceleration. 



An individual showing all the stages is illustrated in fig. 7 of pi. XII. 

 In this specimen about two whorls are in the tnhcrculosiis stage, fol- 

 lowed by one and a half whorls with parisicnsis characteristics. A 



