54 Mr. J. Hopkinson on the 



IX. — On some Points in the Morphology of the Rhahdo- 

 phora^ or true GraMolites'^ . By JoHN HOPKINSON, F.L.S., 

 F.G.S. 



Peofessoe M'Coy, in his ' British PalfBozoic Fossils,' pub- 

 lished in 1854, in describing- a graptolite from the Sldddaw 

 Slates and other beds, to which he gave the name of Grapto- 

 lites lathis, speaks (p. 4) of " transverse diaphragms " being 

 present near the base or proximal termination of the calycles 

 (hydrothecffi), and shows the position of these diaphragms in a 

 figure (pi. 1 B. fig. 7) which probably represents part of a 

 branch of Diihjmograiitus j^otuhis or an allied species ; but it 

 is impossible to refer with certainty to any one species his 

 aggregate Graptolites latus, now universally admitted to have 

 been founded upon fragments of branching forms. 



No further allusion appears to have been made to the pre- 

 sence of any dia])hragms or septa until, in 1868, I stated 

 (Journ. Quekett Microsc. Club, vol. i. p. 161) that I could 

 find " no indication of a dividing septum " in graptolites '' if 

 we except a few forms in which there is an impressed line 

 between the hydrothecaj and the periderm " (perisarc), which 

 I then compared to that " at the base of the hydrotheca? in the 

 Sertulariadaj." I accepted, however, the generally-received 

 view that the graptolites agree with the Hydrozoa in their 

 hydranths not having been cut off from the common ccenosarc 

 by an actual entire or perforated septum, differing thus in their 

 structure from the majority of the Polyzoa. 



More recently Professor Allman, in his ' Monograph of the 

 Calyptoblastic or Tubularian Hydroids' (Ray Society, 1872), 

 not admitting the presence of any septum or constriction, has 

 compared the calycles of the Rhabdophora to the fixed nemato- 

 phores (sarcothecffi) of the Plumularida?. He observes (p. 179) 

 that '^ the denticles of the graptolite have their cavity unin- 

 terruptedly continuous with that of the main tube, there being- 

 no diaphragm or constriction of any kind at the point where 

 the one passes into the other ;" and, alluding to Prof. M'Coy's 

 observations already mentioned, he says that he " speaks of a 

 septum at the base of the denticles in certain graptolites, but 

 subsequent observations have not tended to confirm this 

 statement." 



I have recently had the opportunity of examining an ex- 

 tensive collection of grajitolites made by Mr. W. Kinsey 

 Dover, F.G.S., from the iSkiddaw Slates, mostly from Skid- 



* Read before the Eritisli Assoeiation (Section C), York, Sept. 7Ui, 

 1881. Au abstract appeared iu the ' Geological Magaziue' for October. 



