150 ANNALS NEW YORK ACADEMY OF SCIENCES 



elongated and relatively thin are observable and they rise from the same 

 terminal expansions characterized by irregular shape, fringed margins, 

 corroborating ribs and rootlike filaments, all that as changeable as re- 

 quired by the nature of the point of fixation. I mention, especially, 

 Paramuricea borealis (from 200 fathoms) and Acanthogorgia armata 

 (from 160 fathoms), from the Gloucester fisheries. The last, a large, 

 dendroid form, is furnished with a basal stem extending distally into a 

 rather thin, irregularly shaped expansion which adheres by means of 

 two dependent lobes to the rounded edge of a bowlder about four inches- 

 long. The similarity of this attaching instrument to that of the Dictyo- 

 nema figured plate XXI, 3&, is of great significance. According to my 

 opinion, the only reason that we have not yet succeeded in finding actual 

 fixation of the Dendroidea lies in the fact that the sediments of those 

 places on which the dendroids actually flourished were not favorable for 

 preserving the delicate graptolites, while in the common "graptolite 

 shales" we do not have the sediments on which the Dendroidea actually 

 grew, an assumption strengthened by the mode of embedment discussed 

 in the next chapter. 



To get the significance of the foregoing statements, I may explain 

 them in the following manner: Of all distinct varieties from Navy 

 Island, those which tend to a callograptoid and clenclrograptoid aspect 

 also present the greater part of adhesive organs; these are not confined 

 to the gerontastic stage and not separable from the nemas; the great 

 variation of basal organs imply a similar variation of habitat. 



Here, too, we must bear in mind the results of the last fifty years' 

 work, as follows : 



Supposed Cambrian ancestors of Dictyonema, with sicula, planctonic. 



Earliest Ordovician, Dictyonema flabelliforme ; young stages with long flexible 

 nema and thin adhesive disk, ephebastic stages generally with free sicula, 

 one variety sometimes sessil and that possibly beginning in neanastic stage. 



Later Beekmantown, Callograpti - s ; free sicula? sometimes observed, particu- 

 larly in young stages, later robust stems or hydrorhiza commonly occur. 



Later Ordovician and Silurian, Dictyonemas; no nema and almost no trace of 

 a free sicula observed; on D. cavernosum branching stolons with buds; 

 on the whole, 12 species 24 are known provided with organs adapted for 

 constant fixation. Odontocaulis ; robust main stem, from which new theca? 

 arise. On almost all other genera of the Dendroidea, especially Dendro- 

 graptus no free sicula known, an abundance of organs of attachment de- 

 scribed. 



23 Compare C. salteri, graoaui, elegans, radicans. 



24 Dictyonema areyi, bohemicum, cavernosum, crassibasaJe, (Jesmoidea, leroyense, paral- 

 lelum, percrassum, polymorplmm, subretiforme, stenactinotum, tenellum. 



