660 



NEW YORK STATE MUSEUM 



Fig. 59 T e 1 1- a g- r a )i t u s s i m i 1 i s 

 HuU up. Young- compressed rhab- 

 dosome seen from the under side. 

 Shows the apertures of the sicula 

 and first two thecae. Deep kill. x6 



accordiDg to Gurley it is found in the Main Point Levis or Tetragraptus zone. 

 Ami cites it also from two localities near Levis together witli D i d y m o - 

 g r a p 1 11 s b i f i d 11 s . Li 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 Phyllograptus shale at Krekling, Christiania, Norway ; from the Tetra- 

 graptus zone of Scania by TuUberg ; and the gray Orthoeeras 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/5 of the Bohemian 

 Lo^ver Siluric, the occurrence of this species in 

 Bohemia having before been reported by Tornquist; 

 in Australia, finally, it has been recognized by the 

 younger Etheridge in the auriferous graptolite shale of Victoria. 



Remarhs. Specimens in >vhich 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 Hall as Phyllograptus si mills, a name which was withdrawn later 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 

 similis. Since the latter belongs to another 

 genus (Didymograptus), the term T. similis 

 would, according to the present rules of priority, 

 have to stand against the later and generally 

 adopted name, T . bigsbyi. 



Our list of synonyms demonstrates that several authors have referred 

 this species to Salter's Didymograptus c a d u c e u s . We shall show 

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

 Didymograptus and a fragment of T . similis Hall ; and that according to 

 the rules of priority his name "will have to be applied to the first figured form, 

 i. e. to Didymograptus c a d u c e u s . In no case can Salter's name 

 be employed to designate this tetragraptid. 



Pig. 60 Tetragraptus similis 

 Hall sp. Proximal portion of rhabdo- 

 some. Obverse view. Deep kill. x4.5 



