Dr. H. A. Nicholson on Helicograpsus. 23 
Conclusion. 
Sufficient has now been adduced to settle most satisfactorily 
the question at issue between Dr. Carpenter and myself as to 
the characters of Syringothyris cuspidata, as it may now be 
called. 
The idea that the canaliferous septum and perforations are 
diagnostic features of the typical species of a certain genus, 
and that their absence distinguishes the type of another, both 
species being ‘ undistinguishable by external conformation,” 
must be unreservedly abandoned. ‘The various evidences and 
considerations herein brought forward are totally opposed to 
any isomorphism of the kind; nay, the simple fact of a speci- 
men, like Professor Harkness’s, contaiming a well-developed 
canaliferous septum, but no perforations, is alone demonstra- 
tive of its complete fallacy. It may therefore be safely as- 
sumed that Syringothyris cuspidata and S. typa are one and 
the same species*. 
Il.—Notes on Helicograpsus, a new Genus of Graptolites. 
By Henry ALLEYNE NicHoxson, D.Sc., M.B., F.G.S. 
THE Graptolite for which I propose the above generic title 
was originally described by Hall, from the Hudson-River 
group, under the name of Graptolithus gracilis (Pal. N. York, 
vol. 1. p. 274, and vol. iii. pp. 510-513). The first specimens 
which were discovered in Great Britain were obtained by Prof. 
Harkness from the Upper Llandeilo rocks of Dumfriesshire 
and Wigtonshire, and were described by him under the name 
of Rastrites Barrandi (Quart. Journ. Geol. Soc. vol. x1. p. 475). 
More recently it has been placed by Mr. W. Carruthers in his 
genus Cladograpsus, under the name of C. gracilis (Geol. Mag. 
vol. v. p. 130). Having, however, had the opportunity of ex- 
amining an extensive suite of specimens, obtained by Prof. 
Harkness and myself from Glenkiln Burn, in Dumfriesshire, 
I still adhere to the opinion which I expressed some time ago, 
that it is unquestionably unique in its characters, and “‘ should 
form the type of a new genus”’ (Geol. Mag. vol. iv. p. 258). 
Gen. Char. Frond bilaterally symmetrical, composed of a 
non-celluliferous stem or “ funicle,” which is curved into the 
shape of the letter 8, and gives off simple monoprionidian 
branches from the two convex portions of the curve, so that 
* Tt will necessarily follow that Martin’s specific name, having priority, 
must be adopted in preference to the one proposed by Prof. Winchell. 
