510 NEW YORK STATE MUSEUM 



Jaekel sketched the mode of existence of the graptolites very decidedly 

 in 1889, asserting that they formed meadows at the sea bottom and fixed 

 themselves with a network of root fibers. His arguments for this conception 

 were, that the graptolites can not have been free-swimming for the reason 

 that their colonies were too heavy to be carried by the water; that they 

 would have had either to move by concerted movements of the zooids, against 

 which the independence of the thecae and of their apertures, and the form of 

 the rhabdosomes militate, or that they would have had to use a hydrostatic 

 apparatus. In the latter case, the central disk would have to be regarded as 

 that organ ; it would then, however, have been floating above the colony and 

 the thecae would have been directed downward, which is considered as 

 unnatural. 



The same conception of the mode of existence of the graptolites was 

 attained by Wiman [1895, p.68] by the following considerations. The 

 graptolite beds can not have been deposited in the shallow littoral regions 

 on account of their thin bedding, they can not be supposed to be deep sea 

 deposits, and are hence, by exclusion, deeper littoral deposits. The grapto- 

 lites were however not pelagic, as the occurrence in these beds of deeper 

 origin might suggest, for then they would occur as frequently in limestones 

 as in shales ; further, on account of the great similarity of their external form, 

 they all must have had the same mode of existence and belonged to the same 

 fauna, but the combined length and stiffness of the nemacaulus, which is still 

 increased by the virgula, as well as the adhering disk of some forms, point to 

 an upright position of the rhabdosome. 



The present writer discovered in the Utica shale complete synrhabdo- 

 somes of Diplograptus and, observing a central bulb, or cystlike organ, 

 described this as having probably had the function of a "float" [1894, p.225], 

 basing his assertion of the floating habit of this genus of graptolites on the 

 great length and thinness of the nemacaulus supporting the rhabdosome, 

 the absence of attached specimens among the numerous synrhabdosomes 

 observed, and the facts of the distribution of the graptolites. 



