630 



THE AMERICAN NATURALIST [\^ol. XL! 



genus with species each showing a distinct step in progressive 

 development, or whether he makes the whole series a variety of 

 something and calls my species subvarieties. But he cannot make 

 the series a variety of Clavilithes parisiensis, any more than he 

 can make the uncle the son of the nephew. 



Professor Boettger will probably find it difficult to point out that 

 the difference between the protoconch of Clavilithes and that of 

 Rhopalithes is due to any difference in physical environment, as the 

 fusoid members of the series, C. rugosus and R. rugoides occur 

 side by side, the same being true of other members of the same 

 series as well. Moreover, if he agrees with Cossmann, that Rho- 

 palithes and Clavilithes are generically identical, he will have to 

 show why the series with the Fusus-like protoconch has columel- 

 lar plaits and why these are wanting in the series with a papillose 

 protoconch. 



Finally I may again call attention to the fact that I have de- 

 scribed in detail the variation in the protoconchs of Fusus and that 

 I have readily admitted the possibility of the existence of larger 

 and smaller initial whorls, of an increase or decrease in the number 

 of whorls in the protoconch, and of the variation in the number 

 of riblets on the protoconch. In fact I have illustrated such varia- 

 tions but I am not ready to admit that there is ever a difference of 

 type in the protoconch in what can otherwise be referred to the 

 same genus. I have repeatedly shown, that the so-called species 

 of Fusus from the American Eocene strata not only disagree 

 utterly as regards the type of the protoconch with true Fusus, but 

 that the young stages as well show much more acceleration than 

 is found in the young of even modern Fusus. ''Fusus apicalis" 

 and ''Fusus houstonensis" are an exception to this and it is not 

 impossible, that in spite of the remarkable protoconch, these may 

 be more nearly related to true Fusi, than is either Falsifusus 

 meyeri or Fulgurofusus quercollis. 



Fusus aciculatus and "Fusus" serratus occur side by side in tlie 

 Calcaire Grossier of the Paris Basin, yet the first retains its normal 

 Fu^iis protoconch wliilc the second hiis a widely different type of 

 protocfMich, Wkv tliat of many ricin-otoinas. It will be difficult 



F. aciculatus retains^he early Fusus whorls, common to all true 



