138 PHYLOGENY OF FUSUS AND ITS ALLIES. 



characteristic of all the phylogerontic species of this and related series 

 is well developed, and the sides are parallel to the axis of the shell. 

 We have in this series the shelved stage following immediately upon 

 the rugosus stage, the latter being represented by the R. angulatiis 

 type of whorl. This was already noted by Deshayes, who stated that 

 the early whorls of this variety were precisely like those of R. angulatus. 

 Two plications occur on the columella. In the specimen figured the 

 ribs still persist as undulations but the spirals are obsolete. In the 

 figure given by Deshayes (pi. 74, figs. 4-5) the ribs have disappeared, 

 but the spirals are still strong. These specimens show different 

 degrees of acceleration. 



Localities: Paris Basin (M. C. Z. 1393) ; Grignon (Desh). 



Horizon: Eocene (Upper?). 



RHOPALITHES TUBERCULOIDES sp. nov. 



(Plate IX, figs. 2T,, 24.) (Type fig. 24.) 



This species occupies the position in the present series which C. 

 tiiherculosus occupies in the Clavilithes series. From five to six 

 whorls have the characters of R. rugoidcs, having all the features 

 found in that species. These are followed by one or more whorls 

 which are free from ribs, and only faintly marked by spirals, these 

 gradually becoming obsolete. These whorls are rounded in outline 

 and furnished with a well-developed sutural shelf which slopes gently 

 outward as in the majority of species of Clavilithes. In the specimen, 

 fig. 23, which is somewhat more accelerated than the type, this shelf 

 appears while the shell is still ribbed, thus paralleling some of the more 

 highly accelerated species of Clavilithes. The posterior canal is 

 strongly developed, and a pseudo-umbilication is produced by the sepa- 

 ration of the inner lip from the columella. 



, Two young specimens of this series are in the siibtuberculosus 

 stage (pi. IX, figs. 18, 19). The first of these is only a step more ad- 

 vanced than the specimen of R. rugoidcs figured on plate IX, fig. 12, 

 in which the last whorl shows a subduing of ribs and spirals and a 

 general rounding of the contours. In fig. 18 the ribs have entirely 

 disappeared but the spirals remain. The sutural shelf is moderately 

 developed and the columella is doubly plicate. The other specimen 

 (fig. 19) is somewhat more accelerated, the ntgosiis stage is shorter 

 and the siibtuberculosus stage is more strongly developed, occupying 

 a complete volution. Two columellar plications occur. It is, of 

 course, impossible to state whether these are the young of R. tuber- 

 culoides or of a form in which a parisiensis stage succeeds the tuber- 

 culosus stage, i. e., R. nocc. 



A specimen from Ully, St. Georges (Acad. Sci. 8026), shows the 

 characters of R. tuber culoides. The last whorl is rounded, without 



