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NEW YORK STATE MUSEUM 



ing and bifurcating rapidly ; in the greater part of the rhabdosome rigid, 

 nearly straight, very closely arranged (about 12 to 14 in 10 mm) and 

 extraordinarily regularly parallel. Width of branches A mm. Interspaces 

 from one to one and a half times as Avide as the branches. Dissepiments 

 very slender, not exceeding .16 mm in width; mostly straight, a little 

 more distant than the branches (about 1 mm) ; the resulting meshes hence 



shortly rectangular. Branches dividing at an acute 

 angle. Thecae not observed. Apertures apparently 

 irregulai'ly disposed, larger ones, approximately corres- 

 ponding in number and position to the dissepiments, 

 separated by more numerous smaller apertures. 



Position and localities. Rare in the horizon with 

 D i p ] o g r a p t u s d e n t a t u s and C 1 i m a c o - 

 g r ap t u s ? a n t e n n a r i u s at the Deep kill. 



RemarJcs. This form is evidently closely related if 

 not identical Avith the species described by Dawson as. 

 D . d e 1 i c a t u 1 u m , which name, being preoccupied 

 by a species name given by Lapworth, was changed by 

 Grurley into D. per exile. However, as Dawson did not furnish any 

 drawings, his short description does not allow any positive identification, 

 and, moreover, as his form has still more closely arranged branches (18 in 

 10 mm) and occurs in another association of species (Phyllograptus 

 typus, Tetragraptus bryonoides and T . b i g s b y i ) , it was 

 not thought safe to identify the form described here with his species. Ami 

 has listed [1888, p.ll7k] a form doubtfully referred to Dawson's species, 

 which he cites, in recognition of the fact that its name was preoccupied, 

 as D i c t y o g r a p t u s n. sp. and records as occurring at the road from 

 Levis to St Joseph with Didymograptus bifidus, D. extensus, 

 D. furcillatus, D. pennatulus, Tetragraptus approxi- 

 matus, T.fruticosus, T . quadri brachiat us and T.serra,and 

 Phyllograptus typus, an association which distinctly points to the 

 next older horizon than that in which our form is found at the Deep kill ; 



Fig. 29 Dictj'onema 

 rectllineatum sp. nov. 

 Enlargement of part of the 

 specimen reproduced on 

 jilate 3, flgure 10. Deep kill. 

 x9 



