6G0 . NEW YORK STA'I'K MUSKUM 



according to Gurley it is found in the Main Point Levis or Teti'agraptus zone. 

 Ami cites it also from two localities near Levis together with Didymo- 

 g r a p t II s b i f i d u s . In Britain it is known from many localities in north- 

 ern England and south Scotland, where it occurs in the Lower and Middle 

 Skiddaw slates. It is further recorded by Brogger from the lower part of 

 the Phyllograplus shale at Krekling, Christiania, Norway ; from the Tetra- 

 graptus zone of Scania by Tullberg ; and the gray Orthoceras limestone of 



Oeland furnished to Holm the material of this 

 species, on which he based his investigation of the 

 structure of Tetragraptus ; Perner describes T. 

 bigsbyi from band Ddl/? of the Bohemian 

 Fig.59Tetrag:iaptus simiiis Lo\ver Siluric, the occurreucc of this species in 



Hall Kp. Young compvessed rhab- ' ^ 



iK%iraper?S;Js''ot'the'"sicufa Bohemia having before been reported by Tornquist ; 



and first two thecae. Deep kill. x6 _ _ • i i • i i 



in Australia, finally, it has been recognized by the 

 }ounger Etheridge in the auriferous graptolite shale of Victoria. 



Reniarhs. Specimens in which the distal ends of the branches had been 

 in contact, either by compression or natural position, had been described by 

 Hall as Phyllograptus si mills, a name which was withdrawn later 

 on by its author on account of the supposed 

 precedence of his species Graptolithus 

 si mills. Since the latter belongs to another 

 genus (Didymograptus), the term T . s i m i 1 i s 

 would, according to the present rules of priority, 



, , , 1 • , ,1 T J J n F'8- 60 Tetragraptus similis 



have to stanci asiainst the later and fjenerally uaii xp. Proximai portion of rhawo- 



~ o ./ some. Obverse view. Deep kill. x4.5 



adopted name, T . bigsbyi. 



Our list of synonyms demonstrates that several authors have referred 

 this species to Salter's Didymograptus caduceus. We shall show 

 under that heading [p.696] that Salter figured under this name a specimen of 

 Didymograptus and a fragment ofT. similis Hall ; and that according to 

 the rules of pi-iority his name will have to be applied to the first figured form, 

 i. e. to Didymograptus caduceus. In no case can Salter's name 

 be employed to designate this tetragraptid. 



