20 /. Hopkinson — On a New Genus of Graptolites. 



they are worth. Hitherto geologists have been proceeding upon the 

 supposition of an ice-sheet and an open North Sea ; but the latter is 

 an impossibility. But if we suppose the seas around our island to 

 have been filled with land-ice during the glacial epoch, the entire 

 Glacial problem is changed, and it does not then appear so sur- 

 prising that ice should have passed over England. 



V. — On Dicellograpsus, a New Gtenus of Graptolites. 



By John Hopkinson, F.G.S., F.E.M.S. 



(PLATE I.) 



THE Graptolites for which the name Dicellograpsus is here pro- 

 posed are usually included in the genus Didymograpsus, which 

 is thus made to comprise two groups of species which are not only 

 generically distinct, but belong to entirely diiferent sections of the 

 Graptolite family, the species properly belonging to Didymograpsus 

 {D. Murchisoni for example) having hydrothecse similar to those of 

 Graptolitlius, while the species erroneously included in the genus 

 (D. Forchliammeri and others) have hydrothecse of the type of 

 Climacograptus. This was first pointed out by Prof. James Hall. 

 In his " Graptolites of the Quebec Group " (p. 57) he removed 

 these species from Didymograpsus, and placed them in his new genus 

 Dicranograptus ; the species previously known as Diplograpsus 

 ramosus being considered the type of the genus. To this species, 

 and to another then first described, the genus was afterwards 

 restricted by Mr. Carruthers, the remaining species being again 

 included in Didymograpsus.^ Though fully agreeing with Mr. 

 Carruthers in thus restricting Dicranograptus, I cannot consider the 

 species removed from it as having any alliance to Didymograpsus. 

 I therefore propose to consider these species as forming a distinct 

 genus, the diagnosis of which is as follows : — 



Genus Dicellograpsus, gen. nov. (from SUeWa, a fork ; <ypa(pQ}, 

 I write). 



Polypary, consisting of two simjole monoprionidian branches, 

 united only at the proximal end, and bearing hydrothecse on their 

 outer aspect ; radicle, or initial process, on the same side of the 

 polypary as the hydrothecse. 



From a slender radicle, flanked by two lateral spines, the simple 

 monoprionidian branches immediately diverge in elegant symmetrical 

 curves ; usually very divergent at their origin, they soon become 

 less so, then spring out again, and continue with a slight inward 

 curve, until, towards their extremity, they are almost straight. 

 They do not appear to be divided by any septum at their origin, — 

 the coenosarc of one branch most probably having been continuous 

 with that of the other. The solid axis, commencing as the initial 

 process, or radicle, bifurcates in the axil of the branches, on the 

 inner or dorsal aspect of which it may in some species be detected. 

 In others it cannot be made out beyond the axil, but from analogy 



1 Geological Magazine, Vol. V., p. 129. 



