628 



THE AMERICAN NATURALIST [Yoi.. XLI 



animal after emergence from the capsule. It is of course possible 

 that this rotation of the axis of the initial whorl may be a result of 

 the rapid increase in size of this whorl since it nearly always accom- 

 panies such rapid increase, in which case it is a secondary feature. 



I have elsewhere^ described in detail the protoconchs of Rhopa- 

 iithes and Clavilithes from the Calcaire grossier of the Paris Basin, 

 and shown their great distinctiveness, the species classed under 

 Rhopalithes having a fusoid protoconch with few riblets, while 

 typical Clavilithes has a papillose one of numerous whorls, with 

 other distinctive characters. I also showed that each genus em- 

 braced a series of species which in their stages of development 

 paralleled each other and ranged from the round whorled, ribbed 

 and fusiform type through a number of progressive changes, to an 

 extreme old age or phylogerontic condition. 1 further pointed out 

 that in spite of this remarkably close parallelism, the generic char- 

 acters remained constant, the protoconchs of the two series remained 

 distinct and Rhopalithes was throughout marked by the presence 

 of columellar plaits (not always ^^sible in old shells unless the lip 

 has been broken back) which never occurred in Clavilithes. More- 

 over, the other shell characters are such that any one familiar with 

 these shells can separate the meml)ers of tlie two sci-ies rdmost at a 

 p;lance antl without reference to the protoconch or (•oliuucilur plaits. 

 In spite of this Cossmann- insists, and Horitgcr follows him — 

 that my distinction is based solt'ly on the (litVerciicc in protoconchs; 

 and that I carry my faith in (1m> ('^^cntial constancy of the characters 

 of the protoconcli and tlicir pliylctic value so far, that 1 have 

 allowed myself to separate into Uxn genera what M. (\)ssmann, 



in their ty[)e-localities, consider to be varieties of one species only. 

 This arraignment might be more serious were ^l. ("ossinann and 

 other high authorities on tlie sliells of the Paris Ba>in acciistonie.l 



early conch sta,J>. M ( ....niann ha^ n.entlN taken to a leco- 

 l.ition of the diveiM- ehaia. l- ..f pn.|..eoneli^. and in hi^ vahiabh' 

 '•Kssii>" ha. iihi^iraled nianv of them 1 nto,tnnanl> tlu-c 



