HAHN, DICTYONEMA-FAUNA OF NAVY ISLAND, N. B. 159 



Among a hundred examples of Dictyonema flabelliforme examined, he 

 failed to observe nemas or disks or any adhesive organs in spite of dis- 

 tinct proximal parts with free siculas. He regards the wrinkling of the 

 rhabdomes as produced merely by pressure, and the early appearing 

 divisions of the nepiastic thecas as due to rapid budding of nourishing 

 thecse. He holds it probable that the early Dendroidea like Dictyonema 

 flabelliforme when derived from graptolites must have possessed thecas 

 like those of Bryograptus hjerulfi. From this point on, he considers 

 that there existed a great difference between the Dictyonema flabelli- 

 forme and the "Dictyonemas" of the later Ordovician and Silurian, as 

 described partly from sections by Wiman and others, and he introduces 

 "Dictyodendron" for the later forms. 



The following objections, however, must be made after careful con- 

 sideration: 1. Young individuals of Callograptus (salteri in Euede- 

 mann's monograph, grabaui as described in this paper) exhibit distinct 

 siculaB and even nemas. 2. True adhesive expansions occur among the 

 Dictyonemas of Navy Island. 3. The tubulose structure is by no means 

 referable to -any kind of stress, because this, when exerted, produces a 

 fine striation, running in parallel fashion over all specimens of one 

 slab, but cutting, of course, the tubes at quite different angles. The 

 associated Staurograptus, moreover, never show a similar structure. 

 4. The young stages of Dictyonema flabelliforme, as fully discussed in 

 the foregoing, are found to be clearly distinct from all stages of Bryo- 

 graptus, as they exhibit a more primitive character (dependent growth) 

 than Bryograptus (declined or horizontal growth of the first branch- 

 lets). Hence the ancestors of Dictyonema flabelliforme were not at all 

 true Bryograpti, but simpler types with features bridging over those of 

 Dictyonema and Bryograptus. 



Thus I feel quite certain that the progress of evolution which Wester- 

 gard believes to have existed between the early Dictyonema flabelliforme 

 and the so-called " Dictyodendron f did really take place among the 

 varietal series of the Dictyonema flabelliforme. 



Finalty, there is one point left which thus far I have deliberately 

 disregarded in order to simplify its consideration, for it adds merely 

 some complications without modifying the preceding conclusion. There 

 is no doubt of the fact that most of the dendroid genera have the charac- 

 ters not only of stadial, but also of collective groups. Of this James 

 Hall was partly convinced even in the '60's, but it has only been recently 

 fully substantiated by the masterly works of Wiman and Euedemann. 

 Among the Dictyonemas, one part has thecse with sharply prominent 



