Notes on Didyniograptus caduceus, etc. 71 



originally founded by Salter on some specimens from Canada 

 submitted to him by Dr. Bigsby,* and was subsequently recog- 

 nised by its describer in the Skiddaw slates of England.! James 

 Hall 1 referred Salter's species to a form which he named Grapto- 

 lithus bigsbyi (a Tetragraptus), and which appears to be regarded 

 by some authors as a synonym of T. bryonoides (T. serra). 



If the reference were correct, then Salter's name should stand 

 and not Hall's, a fact already pointed out by Herrmann. § 

 However, the identity is by no means clear. Salter's figures 

 plainly show a form in which the width of the stipe immediately 

 over the sicula is as great as that of its more distal portion ; 

 while from the minor end of the sicula the prolongation of the 

 virgula, so characteristic of the species, is represented as a fine, 

 hair-like line ; moreover, he begins his description with the words 

 "D. stipite filiformi longo." In Hall's figures, on the other hand, 

 the median process is clearly a third branch, and in no way 

 resembles the delicate thread shown by Salter, and which in our 

 specimens is certaiidy not a Ijranch. 



Professor H. A. Nicholson, in his paper on the Skiddaw 

 graptolites,j| states that from an e.xamination of Tetragraptus 

 bryonoides he is inclined to agree with James Hall, and refer all 

 the specimens in the caduceus form which he has seen to that 

 species. At the same time he says that " whilst it is possible 

 that there may really exist a distinct species with the characters 

 of D. caduceus, Salter, it certainly appears not to occur in the 

 Skiddaw slates, since all the specimens which could l)e referred 

 to this species, when well preserved, show traces of a third and 

 even sometimes of a fourth stipe." At a subsequent datell he 

 found a species in the Skiddaw slates which seems to agree 

 perfectly with Salter's Canadian species. This species he named 

 D. gibberulus. As a justification of his position he says that 



* Quart. Journal Geol. Society, ix., p. S". 



t id., xix., p. 136. 



X Graptolites of the Quebec group, pp. 42, 87. 



§ See Geolog:ical Magazine for 18S6. 



According to Perner (Etudes sur les Grap. de Bohtme, pt. ii., p. 20) thie reference to the 

 species as Tetragraptus caduceus is due to Briigger, but the paper by the latter author is 

 inaccessible to nie, and as Perner's paper only arrived in Melbourne the day before this 

 article was appointed to be read, I have left the reference as it stands. ^■''(-^ l"'^^!- 



Qu.irt .Jour. Geol. Soc, vol. xxiv., pp. 131-133. X' 'C^ ^^J-li/< / ^X 



T Annals and Mag. Nat. Hist. 4, xvi., 271. /c^\^y^e\O^^^L^ / ' 



ARYlg 



