lx BRITISH GRAPTOLITES. 



(1) The true Graptolites (except Dicfyonema and possibly Dendrogmptus and 

 Gallograptus) are all free-swimming forms, whilst the Bryozoa are invariably 

 fixed. 



(2) The undoubted presence of a common canal " in many, if not all." 



(3) The mode of growth and the nature of the embryonic forms. 



(4) The existence of forms like Corynoides. 



He points out that the Graptolites differ from the whole sub-class of the 

 Hydroida in the fact that the polypidom was free, and not fixed by a hydro-rhiza, 

 and he is disposed to place them in a " new sub-class, intermediate between the 

 fixed and oceanic Hydrozoa." 



1867. 

 Carruthers, The same year Carruthers replied to those statements 



" Note on Systematic anc { opinions of Nicholson in much detail, but his paper 



Position, etc., of - • i £ i_ j_i 



contained no new facts or theories. 

 Graptolites," ' Geol. 



Mag.,' vol. iv. 



,ggj, In the same year also a short stratigraphical paper was 



Tornquist. published by Tornquist dealing with the appearance of 



'• Om Lagerfoljden Graptolites in Central Sweden. He considers that Prionotus 



i Dalarnes Under- Sagittarius (His.) and Didymog. virgulatus are identical with 



SiluriskaBildningar." R i udensis . whfle Petalog. folium (His.) is really a Eetiolites. 



Pr. scalaris is founded partly upon Dvplog. pristis and partly upon D. teretiusculus. 



The species discussed, together with Bastrites? convolutus, are recorded by him 



from the Lower Silurian beds of Dalarne. 



In the folloAving year (1868) no less than six papers on 



™ , ' Graptolites were written by Nicholson. The first of these, 



" The Graptolites of "On the Graptolites of the Skiddaw Slates," is mainly 



the Skiddaw Series," descriptive iii character, but the works of previous observers 



' Quart. Journ. Geol. are carefully reviewed, and several new forms of Graptolites 



are named and figured. The following genera and species 



are recorded by him from these rocks : 



Didymograpsus. Salter's Didymog. caduceus (which he considers to be 

 non-existent as a distinct species — at any rate in the Skiddaw Slates — and to be 

 probably identical with Tetrag. bryonoides (Hall) ), D. r-fradus, D. sextans (which he 

 regards as "somewhat peculiar among the Didymograpsi"), D.patulus{=D. hirundo, 

 Salter), D. nitidus, D. bifidus, and l>. serratulus are described, and (1) D.geminus 

 is figured. 



Phyllograpsus. Phyllog. angustifolius, and (2) P. typus. 



Tetragrapsus (Nicholson defends this genus against Hall). T. Headi, T. 

 quadribrachiatus, T. bryonoides, T. crucifer. 



Dichograpsus. Nicholson proposes the retention of Salter's name for this 



