[Annals N. Y. Acad. Sci., Vol. XXII, pp. 135-160, Pll. XX-XXII, 25 July, 1912] 



ON THE DICTYONEMA-FAUNA OF NAVY ISLAND, NEW 



BEUNSWICK 



By F. F. Hahn 



(Presented by title before the Academy, 13 May, 1912) 



CONTENTS 



Page 



Introduction 135 



Given faunula 136 



Astogeny of Dictyonema flabelUforme in comparison with that of Stauro- 



graptus 144 



On the structure of Dictyonema flabelliforme 146 



Mode of life of Dictyonema flabelliforme 148 



On the occurrence of stratigraphical range of the varieties of Dictyonema 



flabelliforme 151 



Significance of the varietal range and its phylogenetic value 153. 



Introduction 



One of the older modes of paleontological investigation, the study of 

 the range and significance of variability, seems now to be somewhat 

 overtaken by and neglected on account of the excellent results obtained 

 in the study of the stages of earliest youth, growth and senescence. My 

 own studies on Jurassic invertebrates, which made me familiar with a 

 vast number of individuals of many species, brought me to the convic- 

 tion that a combination of these two modes of treatment would, in every 

 case where the given material is sufficient, lead to an advance greater 

 than would be possible by either method alone. Thus, when I worked 

 over in the Museum of Columbia University the wonderful collections 

 from the Dictyonema-shales made by G. van Ingen and W. D. Matthew 

 at Navy Island, N. B., from Division III, b, c, commonly regarded as 

 Upper Cambrian, 1 of course my first thought was to see whether I could 

 find any relationship between the range of variability and the history of 

 the races among the Dictyonemas. And this animal association seemed 

 well adapted to this kind of study, for though the Dictyonema-shales 

 contain a vast number of individuals, there are only four species com- 

 mon, two of which are graptolites. 



1 According to the trilobites found in Sweden and England, it must apparently be 

 placed at the base of Ordovician. 



(135) 



