ORAPTOi:iTI0S (.W XEW YORK. I'AU'I' 1 



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and as also occurring at the Cliff facing the foundry at Levis, associated there 

 with the common species of Tetragraptiis and D i p 1 o g r a p t u s 

 d e n t a t u s , an association Avhich would indicate a transitional bed 

 between the horizons of D i d y m o g r a p t u s 

 b i f i d u s and D i p 1 o g r a p t u s d e n t a t u s . 



DESMOGRAPTUS HopkiuSOU 



The name Desmogra})tas was proposed by 

 Hopkinson [1875, p.668] as a subgeneric term of 

 Dictyonenia for forms in Avhich, as in the genotype, 

 D . c a n c e 1 1 a t u s , " the meshes or interspaces are 

 chiefly formed by the branches coalescing and divid- 

 ing by virtue of their curvilinear direction." Tiie 

 flexuous and anastomosing course of the branches 

 forms a character so readily recognized and so dis- 

 tinctive of a group of species, that we have no hesi- 

 tation in recognizing the latter as a genus. This is 

 represented in the Deep kill fauna by two species. 



The presence of occasional dissepiments and of 

 parts with more straightened branches in I) . i n t r i - 

 cat us suggests, however, that the structural differ- 

 ences between Dictyonema and Desmograptus may 

 not be as great as it would appear from their widely 

 different aspects. Of special interest in regard to 



this relationship is the basal part of the specimen, reproduced in figure 30, 

 which shows in the oldest proximal part parallel branches and true, stout 

 dissepiments. This Dictyonema structure rather abru])tly changes into the 

 Desmograptus structure with irregular and coalescing branches, a change 

 Avhich indicates the development of Desmograptus from the typical, also 

 geologically older Dictyonema. 



Fig. 30 Desmograptus intri- 

 catus sp. nov; Enlargement of 

 proximal portion showing transi- 

 tion from straight to undulating 

 branches in lower part. Deep kill. 

 x.5.2.5 



