594 



NEW YORK STATE MUSEUM 



Matthew, who had a large collection of D. f 1 ab elli f o r m e from 

 the St John basin for investigation, considered it as having had a floating 

 mode of existence [1891, 9:85]. When, later, Gr. van Ingen collected some 

 specimens of the same species for him, which had short rootlets [figured 

 1895, pl.49, fig.l and 2], he remarked that "it might appear from such 

 examples as these, that it w^ould be possible to show the existence of a 

 sedentary variety or stage in this species ; still, it does not seem that this 

 condition of the rhabdosome is at all frequent, for among scores that have 



ft"] 



Fig-.23 Dictyonema rarum Wiman. Series of thin sections. t = thecae 

 or nourishing individuals; g-gonangia; k = budding individuals. FromLower 

 Silurio flint-boulders of Gotland. x53. (Copy from Wiman) 



been examined since these ^vere found, none with roots have been detected." 

 It is further suggested that these processes ma}^ have had some other office 

 than that of anchoring the rhabdosome at the bottom, and that 

 they are too short to afford more than a very feeble foothold at the 

 surface of the soft ooze. 



Wiman's investigations have made us well acquainted with the proximal 

 end of at least one species, D. caver no sum. This [fig.24, 25] 

 shows a basal disk, provided wdth radial ribs, which extend into a kind of 

 network that would seem to have been well adapted to fixation on soft 

 ooze. Wiman came indeed to the conclusion that the Dictyonemas, like all 



