Development and Mode of Growth of Diplograptus. 249 



latter was once stiff, it certainly was of advantage to resist 

 breaking so far as possible. While Wiman finds it difficult to 

 imagine how stiff tufts of Monograptidce a meter long could have 

 been suspended, I encountered the same difficulty in trying to 

 imagine how the long and heavy rhabdosome of Diplograptus 

 pristis could have been supported by the very slender and often 

 very long hydrocaulus. I may be also allowed to refer here to the 

 disproportion between the rhabdosome and the thread-like pro- 

 cess of the sicula in Mceandrograptus (Moberg, I. C). The waves 

 were of no danger to the little colony, as the latter probably kept 

 in deeper water. It also would be strange that complete hydro- 

 somes are so rare when they would have been moored and could 

 have been buried in situ; and supposing that the fragility of the 

 rhabdosome forbade the preservation of the rhabdosomes in con- 

 nection with the center, the former ought to be found, at least, 

 often in stellate arrangement. 

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