HISTORY OF RESEARCH. lxxi 



In 1871 Hopkinson published a paper on Dicellograptus, 



jt 7 • a new genus which he proposed for those simple bifurcating 



" On Dicellograptus, a forms which had been previously included along svith others 



New Genus of Grapto- by Hall iii his genus Dicranograptus, but had been retained by 



lites," ' Geol. Mag.,' Carruthers, Nicholson, and others in the genus of Didymo- 



graptus. In the forms assigned to this new genus the solid 



axis bifurcates in the " axil " of the branches ; in one species the polypary is slightly 



enlarged at the axil, in others we get a spine of variable length, while in another 



the branches are connected by a membrane very like the corneous disc of Dicho- 



grapsus. The thecse are the same as in Glimacograptus, " undistinguishable from 



each other for the greater portion of their length." 



Hopkinson discusses the nature of the so-called "axillary spine," which is 

 especially conspicuous in this genus, and which had been regarded by Nicholson 

 as the true " radicle," and also by Carruthers as the true " initial process," while 

 Hopkinson claims that the " proximal spine " (which is usually flanked by two 

 lateral spines) is the true " radicle," and that the " axillary spine " is, so far as we 

 know at present, " an organ without its analogue in any other genus." This was 

 the first recognition of the distinction between what is now known to be the 

 "apertural spine" of the sicula and the apex of the sicula itself, a distinction 

 which has proved to be of first-class systematic importance in this diagnosis. 



Hopkinson also points out the unavoidable confusion in measuring the angle of 

 divergence of the branches resulting from this failure to distinguish between the 

 "initial spine" and the "axillary spine;" and he shows that it is not always 

 possible to measure the angle of divergence along the polypiferous margin, as 

 suggested by Nicholson. 



He believes that in Dicellograpsus, Dicranograptus, and Climacograptus the 

 branches are organically connected where in juxtaposition, " there being no septum 

 observable." 



The following species are included by him in his genus Dicellograpsus : 

 (1) I). Forchammeri, (2) D. elegans, (3) D. mqffatensis, (4) D. anceps, and a new 

 species, (5) D. Morrisi. 



He gives the range of Dicellograpsus as " exclusively Lower Silurian," and he 

 states that it is eminently characteristic of the Llandeilo formation. 



Hopkinson's second paper contained a description of an 

 interesting specimen of Dlplog. pristis collected by the 



Hopkinson, 

 On a Specimen of 



Geological Survey of Scotland from Leadhills, bearing " repro- 



Diphgrapsus pristis ductive capsules." These reproductive organs, which he 



with Eeproductive considers " represent the gonothecse of the recent Sertularian 



Capsules," ' Ann. and Zoophytes," appear to have budded from the periderm at 



Mag. of Nat. Hist.,' • -^ angles to the thecse. They are pear-shaped and 



ser. 4, vol. vii. e> & J I . 



" bounded by a single marginal fibre slightly thickened at its 



