518 Notices of Memoirs — O. R. Vine on Fossil Poly zo a. 



cia ; " ^ bis own opinion, however, was very decidedly expressed. 

 " The point I would chiefly call attention to is that there is a com- 

 plete series up to the most compound in this remarkable family ; " 

 and after pointing out the varied features of the leading types of the 

 GraptolitidcB, he concludes by saying, " Dendrograptus has the branches 

 numerous, unsymmetrical, and crowded, wbile Didyonenia completes 

 the series by showing the numerous rod-like stems each with their 

 cells in double rows, connected by numerous transverse bars into a 

 network like that of Fenestella, to which, indeed, I believe it forms 

 the passage group." ^ Professor Nicholson, after examining in detail 

 the various points raised by Mr. Salter, says, " The ' polyzoarium ' 

 (of the Polyzoa) is commonly more or less highly charged with 

 lime, and this is especially the case with the fossil forms. The 

 polypary of the Graptolites, on the other hand, are invariably 

 corneous (or chitinous)."^ Notwithstanding these varied opinions, 

 I very reluctantly reviewed the whole of the points mooted by 

 Nicholson and others, and then submitted my notes to Mr. Lap- 

 worth's scrutiny before publication. He has gone over every one 

 of these notes critically, and, as his decision is adverse to my own 

 views (founded to a large extent upon facial resemblances), I can- 

 not do otherwise than bow to his dictum. " If the Polyzoa and the 

 Graptolithina had a common ancestor — a view I have always been 

 disposed to adopt myself — it must have existed at an antiquity far 

 more greatly removed from Silurian time than Silurian time is from 

 our own ages; for the differences which then separated the two 

 groups appear to have been almost as gigantic in importance as 

 those which divide the Hydrozoa and Polyzoa of the present day.* 



For the purpose of comjDarison I append a list of the leading 

 genera of the Graptolites with the genera of Polyzoa found in the 

 same formations. 



Vertical Eange of Graptolites, according to Nicholson, Lapworth, and 

 Catalogue op Cambrian and Silurian Fossils, School op Mines. 



(L.) Lapworth. (N.) Nicholson. (S.M.C.) School of Mines Catalogue. 

 Formation. Genera only given, with corresponding increase of Polyzoa. 



Cambrian. Oldhamia ardiqua, Forbes; O. radiata, Forbes (S.M.C. p. 8). 



Upper Lingula Dictyonema sociale, Salter (S.M.C. p. 12), also in Tremadoc slates 

 Flags. (N.) 



Arenig and Dichograptus, Didymograptus, Tetragraptus, CKmacograptus, Diplo- 

 Llandeilo. groptus, Grapfolithus, Rastrites, Dictyonema? PhyJlograptus, 



Graptolithus (S.M.C. pp. 17-18), Trigonograptus, Ftilograptus, 

 Dendrograptus, Callograptus, Dictyograptus (Lap.). Polyzoa: 

 Phyllopora, Ptilodictya (Lower Llandeilo), Branching polyzoon 

 (S.M.C. p. 20), hardly distinguishable in form from Grapto- 

 lithina, only it is calcareous. 



Up. Llandeilo. Didymograptus, Tetragraptus, Climacograptus, Diplograptus, Dicra- 

 nograptus, Graptolithus, Rastrites, Dictyonema, Protovirgularia, 

 Helicograptus, Pleurograptus, Dicellograptus, Cyrtograptus (S.M. 

 C. pp. 23-24). Polyzoa : Ptilodictya and Fenestella ? n. sp. (Ibid. 

 p. 28). 



1 Geological Memoirs of North "Wales, p. 328, 1866. 



^ Ibid. 3 British GrfqitoUtidm, p. 85. 



* Concluding remark in Mr. Lapworth's letter to me, May 16, 1881. 



