New Horizon in St. John Group. 341 



D. flabelliforme. Mr. Salter fully understood the cup-like 

 form of the species which he described and its relation to 

 the graptolites, and his name well expresses the multitudes 

 of these delicate organisms which are exposed in breaking 

 open layers of the Dictyonema shale. 



For a long time the idea prevailed that this organism was 

 rooted in the mud and grew on the sea bottom. One author 

 speaks of the lower part of the hydrosome as a kind of cage 

 buried in the mud, which supported the cup in an upright 

 position, but it does not seem at all clear that Dictyonema 

 was in any way thus attached. The sicula or initial point 

 is altogether too small and slight to give support to the 

 structure growing from it, and the living cells begin im- 

 mediately above the sicula, and therefore, it is improbable 

 that the lower part of the hydrosome was buried in the 

 mud. Dictyonema seems rather to have been a free 

 organism, floating in the ocean, and perhaps capable of 

 moving by means of cilia? or fleshy appendages which have 

 not been preserved. 



Dictyonema began life as a Bryograptus, if we may judge 

 by the appearance of the hydrosome, which did not develop 

 connecting threads on the primary branches, and usually 

 not until the growth of the secondary branches was com- 

 pleted. Then gradually and more numerously as the 

 hydrosome grew, the cross threads appeared. 



It is in keeping with this that Dictyonema was not the 

 first form of the Graptolite family that appeared. Beside a 

 few poorly preserved forms of the Lower Cambrian rocks, 

 there were in Sweden and Acadia two genera of graptolites 

 which either preceded it or appeared with it ; these are 

 Trichograptus or Clonograptus, and Bryograptus. 



G. Linnarsson discovered a graptolite in West Gotland, 

 which he referred to Dichograptus. It is a small, slender 

 form with distant cells, which, by H. A. Nicholson, has 

 been referred to Trichograptus, and by O. Hermann to 

 Clonograptus. The species was found with the trilobite 

 SpJverophthaimus alatus, and therefore, should be older than 

 the Dictyonema schists. 



