748 NEW iORK STATE MUSEUM 



PLATE 1 



Genus dictyonema Hall 



See pl.3 



Dictyonema flabelliforme Eichwald (sp.) 



Page 599 



1-19 Astogenetic growth stages 



1 Sicula with very long nema. x5 



2 Sicula with budding first theca. x5 



3 Sicula and first theca matured, showing the divergence of the latter. x5 



4 Idem, from the other side, showing the origin of the first theca near the 



apex of the sicula. x4| 



5 Young colony with two thecae. x5 



6 Another view of a like growth stage in which both thecae strongly 



diverge, x5 



7 A specimen of the same growth stage showing the point of origin of the 



second theca. x5 



8 A young colony (rhabdosome) with three thecae, two of which appear to 



be of composite nature. x5 



9 Another aspect of a like stage showing also the composite nature of one of 



the thecae. x5 



10 Young rhabdosome with nema and primary disk. x5 



11 Young rhabdosome in which the first dichotomy of a branch has taken 



place. x5 



12 Young rhabdosome showing several bifurcations, the further growth of 



the branches and the form of the thecae, x5 



13 A little more advanced" rhabdosome with the first dissepiment. x5 



14 Young colony seen from the under or theciferous side, exhibiting the 



thecal apertures. x5 



15 Same view of a somewhat older rhabdosome. The aperture of the sicula 



is seen in the center. x5 



16 Young rhabdosome seen from the upper side. x5 



1 7 Same view of a somewhat older colony. x6 



