CONTRIBUTIONS TO PALiEONTOLOGr. 



81 



These forms, and the great variety which are observed all ap- 

 proximating this one, appear to have been the growth of the frond 

 above the more regularly spiral portion, where the axis, becoming 

 more free and rapidly ascending, has permitted these irregular 

 expansions of the parts. 



Forms like this one are of common occurrence in the arenaceous shales 

 of the Hamilton group in Otsego and Madison counties : they are less 

 conspicuous in the softer calcareous shales of Cayuga, Seneca and Ontario 

 counties. 



The regular spiral portion of the frond of this species has not come under 

 my observation in the localities where these specimens were obtained ; but 

 a similar or identical species, in regular form, occurs in the same position 

 in Schoharie county. 



I should not omit to observe that with the S. typum in the softer shales 

 are similar irregular expansions, but of less vigorous growth than those 

 here noticed. Nor is it impossible that the differences of condition, and of 

 the sediment, may have produced in a single species those modifications 

 which I am at present compelled to recognize as specific differences. 



Fig. 3. Spirophyton velum : Vanuxesc. 



[Senate, No. 115 J 



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