224 Eeport of the State Geologist. 



of the Quebec forms or of Dichograptus Kjerulfi^ Herrmann, 

 from the Norwegian Phyllograptus shales ; but the central discs 

 of the two species of Dij)lograj>tics seem to me to be relatively 

 much too small to carry the whole colony.* 



The Basal Cyst. 

 In a preliminary notef a basal organ, appearing in most fossils 

 only as a subquadrate impression, has been described as a ^' pneu- 

 matocyst." The latter is often so large as to overlap the other 

 central parts and even tlie proximal ends of the rhabdosomes. 

 It appears only as an impression in specimens which have the 

 central disc and funicle well preserved as chitinous bodies (cf. 

 PL I, figs. 6, 7, 8, 10 ; PL II, figs. 1, 2, 3, 5) ; in very fair speci- 

 mens it exhibits only a filiform chitinous border, while in a few 

 (cf. PI. Ill, figs. 9, 19) the test itself is visible. It must be in- 

 ferred from these observations that the test was comparatively 

 thin. The impressions or the scant remains of the periderm 

 would naturally not have been sufficient to be made the object 

 of a description if there had not come under observation, in a 

 number of specimens, large prominences which show that the 

 organ consisted of two segments resting in the middle on both 

 sides of a subquadrate base. This base is formed by a neatly fur- 

 rowed plate represented in PL II, fig. 1. The prominences con- 



* I have used so far, on account of some citations from the first authors on GraptoUtes, the old 

 nomenclatui-e, especially as Introduced by Hall. As there are now, however, terms In use which 

 are taken from the Zoology of the Hydrozoans, such as hydrotheca and hydrosoma, I intend to use 

 more zoological terms which, I believe, will facilitate the description and prevent misunderstandings. 



There is no doubt that the use of the term hydrotheca, if the comparison of the GraptoUtes with 

 the Hydrozoans Is accepted at all. Is proper, though the term f/ieca is preferable. T)ietevva.hydro8oma, 

 however, means In the terminology of the Hydrozoans, as Introduced by Allmann (George Q. Allmann, 

 A Monograph of the Gymnoblastldae or Tubular Hydrolds, vol. I, 1871), " the whole colony." This 

 hydrosoma includes the trophosoma, i. e. " the entire assemblage of zoolds with their connecting 

 basis destined for the nutrition of the colony," and the gonosowia, the entire assemblage of zoolds 

 destined for the sexual reproduction of the colony. As we shall see, the compound colony of Diplo- 

 graptus contains a central verticij of gonangla which constitutes the gonosoma, the remainder, i. e., 

 the central organs and the assemblage of stipes, branches or polyparles, constitutes the trophosoma. 

 It is evident that the use of the term "hydrosoma" for a stipe would be a synecdoche, the 

 putting of the name of the whole for a part. This difficulty could be avoided by using the term 

 " rhabdosoma," now used generally In the excellent papers on GraptoUtes of the Swedish palaeon- 

 tologists. 



Another misunderstanding may arise from the use of the terms axis and virgvla for the stem 



which fastens the rhabdosome to the funicle. In the description of the single rhabdosome it is 

 usually mentioned that the virgula is prolonged " distally," or toward the center. This prolongation 

 forms the connecting stem, and Is a canal containing, as we shall see in another chapter, in young 

 stages, the virgula of the rhabdosome Inclosed in its distal part (cf. PI. II, fig. 6). The stem Is, there- 

 fore, not the prolongation of the virgula alone. The application of the zoological term hydrocaulus 

 for this canal would dispense with the necessity of referring the latter to any part of the rhabdosome. 



+ American Journal of Science, loc. cit. 



