244 Report of the State Geologist. 



of the rhabdosome would exclude the pre-existence of the 

 common canal in the hydrocaulus. Therefore the interesting 

 question arises : What became of the hydrocaulus of the sicula ? 

 I hope that my material of young rhabdosomes with hydrocauli 

 will permit an answer to this question later. 



GeNEEAL APPEA.BANOE OF THE CoLONY AND ItS SYSTEMATIC " 



Rela^tions. 



The restoration of the colonial stock of Diplograptus given in 

 Plate II, fig. 5, was drawn with the assumption of a floating 

 mode of life in Diplograptus. Since then material has been 

 found (cf . PL Y) which does not justify such a supposition, and, 

 therefore, the writer presents this sketch only as an illustration 

 of the relative vertical succession of the parts, without regard to 

 the question of their absolute position, for there is a possibility 

 that the order was the reverse of that given in the figure, and 

 that the basal cyst was the undermost part of the colony. 



It is a fact of special importance that the uniform association, 

 stated by Allmann, 1. c, of the horny receptacles of the 

 hydranths (hydrothecse) with the horny receptacles of the genera- 

 tive organs (gonangia) among the Hydrozoa, is also found in 

 Dijplograptus. As this association is the specific character of the 

 Calyjptohlastea {PlumularidcB and SertularidoB)^ its observation 

 on Diplograptus would seem a strong argument for placing 

 Diplograptus near the CalyptoUastea. But in spite of this 

 homology between Diplograjptus and the Sertularians in par- 

 ticular, the former, like the other Graptolites, has to be separated 

 from the Sertularians on account of the horny sheath of the 

 embryo, and, what seems more important, the horny axis of the 

 rhabdosome.* These differences justify the grouping of the Grap- 

 tolites into a separate class, the Rhabdojphora. 



It is my pleasant duty to express my most sincere thanks to 

 Profs. James Hall, John M. Clarke, C. E. Beecher and R. P. Whit- 

 field, who, by their kind advice and by generously placing at my 

 disposal literature and collections, have enabled me to complete 

 this paper. 



* Allmann.fltates, as another distinction, the differing communication between the hydrotheca and 

 central cavity. The living Hydrolds have only a constricted point of communication or even an 

 Imperfect diaphragm, while the point of communication of the Graptolites is regarded as not con- 

 stricted, though the latter needs verification, as there are indications of a slight constriction in some 

 species. For instauce. Tullberg observed, In slides of Diplograptus 2)almeus, Barr., that " the thecal 

 partitions are in all sections well marked and provided with thickened inner edges." 



