158 ANNALS NEW YORE ACADEMY OF SCIENCES 



Diet yog rapt us Dictyonema 



"Cells: Well-marked; tend to become "Cells: Small, generally disposed at 

 uniserial. angles of about 120°. Crinkly lon- 



gitudinal ornament appears. 

 "Sbape: Like a fisherman's net from "Shape: Basketlike, starting from a 

 a sicula of no great length with long narrow tube or nema and di- 

 primary branches, diverging at an verging at angles which in the later 

 angle rarely greater than 90°. forms approach 160°. 



"Dissepiments : Their development "Dissepiments : Their importance, in- 

 ever more and more delayed until crease and the general aspect of 

 they become practically abortive. the later forms is that of a square 



or rhomboidal mesh in which cross 

 bars and stipes are of approxi- 

 mately equal importance. 

 "Type : var. acadica forma typica." "Type : var. noi'icegica." 



There is one point in which I completely agree with this author, viz : 

 the importance of the differentiation among Dictyonema flabelliforme. 

 We both believe in this as the point of generic divergence ; but in detail, 

 I cannot help stating that all my observations run along the opposite 

 direction. I merely recur to the facts that 



Yar. conferta, restricted to a lower horizon, according to the sugges- 

 tions of Matthew, Fearnside and the majority of the Scandinavian 

 authors, shows clearly the tubulose structure and mode of growth and 

 dissepiments of "Dictyonema" and the projecting cells of "Dictyo- 

 graptus." 



Var. desmograptoidea has cells, mode of growth like "Dictyonema/' 

 cross-threads like "Dictyograptus." 



Var. acadica has cells, sicula, like "Dictyograptus," tubulose structure 

 like "Dictyonema." 



Var. norwegica has cells like "Dictyograptus/' dissepiments like 

 "Dictyonema." 



Var. ruedemanni has sicula, dissepiments, structure like "Dictyo- 

 graptus/' cells and growth like "Dictyonema." 



Hence, as all the known varieties are in part distinguished by the 

 features of "Dictyonema" and in part by those of "Dictyograptus" such 

 a separation, of course, seems impossible. Furthermore, the ancestors 

 were doubtless bryograptoid with very distinct cells, without numerous, 

 dissepiments. Nor did Westergard agree with Fearnside's assumption,, 

 so that against this hypothesis there appears to be no further objection- 

 necessary. 



On the other hand, Westergard, from whose detailed work my own 

 observations do not differ widely, starts with the following suggestions: 



