PIIYLOGENY OF FUSUS AND ITS ALLIES. 1 39 



ribs but with a shelf and a slight depression or concavity below this. 

 The spirals are strong. The penultimate whorl is similar, but without 

 the shelf. Four distinct plications are seen far back on the columella. 

 The subsutural band is prominent. 



Another specimen from Parncs in the same collection (6897) is 

 quite remarkable, in that it retains its ribs even onto the final whorl. 

 The last of the ribbed whorls have a well-developed sutural shelf. 

 The spirals also remain strong. This is a case of partial acceleration 

 in which some of the features which normally should have disappeared 

 are still present. 



Localities: Paris Basin (M. C. Z. 1397, 27784, 27774, 1390, 27728, 

 type) ; Ully, St. Georges (Acad. Sci, 8026) ; Parnes (M. C. Z. 27788, 

 Acad. Sci. 6897) ; Chaussy (Amer. Mus.). 



Horizon: Middle Eocene. 



RHOPALITHES NO^ (Chemnitz). 



(Plate XVI, figs. 1-8.) 

 1795. Murex nocc Chemnitz, Conch. Cabin., vol. XI, p. 296, pi. 212, figs. 2096, 2097. 

 1803. Fiisus noce Lamarck, Ann. du Museum, t. II, p. 317. 

 181 5. Fusus iiocE Lamarck, Tab. Encj-cl. Meth., pi. 425, fig. 5. 



1823. Fusus noa Lamarck, Rec. de Planches des Coq. Foss. Env. Paris, pi. IV, 

 figs. I, 2. 



1824. Fusus nocc Deshayes, Coq. Foss. Env. Paris, T. II, p. 528, pi. 75, figs. 8, g, 

 12, 13. 



1866. Fusus nocB Deshayes, Anim. sans Vert., p. 257. 

 1889. Clavilithes noce Cossmann, Cat. Coq. Foss. Env. Paris, p. 174. 

 See also: 



1896. Fusus (Clavella) noce var. orangustatus Gregorio, Ann. de Geol. et dc Pal., 

 Liv. 21, p. 45, pi. 4, fig. 14 a-c. 



This species is the parallel of Claz-ilithcs suhscalaris. It always 

 possesses a rngoidcs stage, the young being indistinguishable from 

 R. rngoidcs. This stage varies in the number of whorls which it 

 possesses, these being fewer in the more accelerated individuals. There 

 is also some variation in the strength of the ribs and the angularity 

 of the periphery of the whorls which is often accentuated by the 

 strengthening of the peripheral spirals and the concomitant retention 

 of the shoulder striae. The strong development in accelerated indi- 

 viduals of the subsutural band gives the shoulder a concave appearance 

 which further accentuates the angularity of the periphery. These 

 variations are of the same character as those found in R. rngoidcs. 



One of the characteristic features of R. nocc is the persistence of 

 the spirals on the body-whorl after the acquisition of the adult char- 

 acteristics. On the whorl itself they are somewhat subdued, but on 

 the spindle they are as a rule very strong. 



The specimens illustrated on plate XVI show some of the chief 

 varieties of this very variable species. These varieties owe their 



