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, containing 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 cusjpidata and S. typa are one and 

 the same species*. 



II. — Notes on Helicograpsus, a new Genus of Graptolites. 

 By Henry Alleyne Nicholson, 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 Grajptolithus gracilis (Pal. N. York, 

 vol. i. 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. xi. p. 475). 

 More recently it has been placed by Mr. W. Carruthers in his 

 genus Gladograpsus^ under the name of G. 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 S, and gives off simple monoprionidian 

 branches from the two convex portions of the curve, so that 



* It will necessarily follow that Martin's specific name, having priority, 

 must be adopted in preference to the one proposed by Prof. Winchell. 



