158 Tlte Life-Hisiory of Spirifer I(ei'is. 



of the form, the coitcretionari/ structure of the beds, and the 

 relative abundance ot the individuals in the case of both species 

 {S. bicostatus and S. Icevis). Hall speaks of the only locality in 

 which he has discovered this peculiar form, as *'Vanuxeni's lo- 

 cality in Oneida Co." He finds them on the surface of a thin 

 layer of limestone. Vanuxem describes the species as occuring 

 in "slate" (shale?); and as in the case of *S'. Icevis, so of S. bicos- 

 tatus, Hall failed to find perfect specimens. 



The distinction observed by Hall, and upon which he bases 

 the specific identity of ^S'. bicostatus, is the absence or i)artial 

 obliteration of the radial plications; when present, these are 

 obscure or at the margins. 



This character, only carried to a greater extreme, is recognized 

 in S. IcBvis. However, as far as my observation goes, the presence 

 of plications at all, in the latter form, is confined to a few over- 

 large individuals occurring in the lowest known layers in Avhich 

 the species is found. I have not seen the character on any spec- 

 imens occurring in strata above that in which it first appears. 

 Whenever the plications are present, they appear as rather faint 

 undulations of the margin, extending rarely as far as half way 

 to the beak. May we not reasonably regard them as the trace of 

 ancestral plications, seen as a variable character in S.Jimbriatus, 

 here becoming obliterated? It is not the beginning of a new 

 character, but the dropping of one of the typical, though variable 

 characters of the old but still continuing race. 



When we look forward to the Carboniferous representative 

 Ave see S. glaher, with occasionally a trace of plications on the 

 margins (see Davidson's monograph). The smooth uuplicated 

 form is a v'arietyof one Avhich was typically plicated. S. crispus 

 and its full complement of vtirieties appear, so far as this char- 

 acter is concerned, to run through all grades of development at 

 the very outset among the Niagara rejiresentatives. 



Hall also speaks of the shorter hinge-line, and the abrupt curv- 

 ing of the strise at the extremities, —two characters which are 

 associated with each other,— a fact suggesting their relation 

 (See Plate XIV.). We explain it in the following way : — 



We presume that normally, as in the typical form, there is 

 greater lateral extension of the hinge-line than in the unplicated 

 forms, — and Avith this character, a straightening out of the con- 



