GKAPTOLITES OV XEW YOItK. I'AIM' 1 



GOO 



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

 with the common species of Tetragraptus and Dipl ogra p tiis 

 dentatus, an association which would indicate a transitional bed 

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

 b i f i d u s and I) i p 1 o g r a p t u s dentatus. 



DESMOGRAPTus Hopkiuson 



The name Desmograptus was proposed by 

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

 Dictyonema for forms in which, as in the genotype, 

 D. cancellatus, *' the meslies or interspaces are 

 chiefly formed by the branches coalescing and divid- 

 ing by virtue of their cui'vilinear direction." Tlie 

 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 D . i n t r i - 

 c a t u s 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 I'elationship is tlie basal part of the specimen, reproduced in figure 30, 

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

 dissepiments. This Dictyonema structure rather abruptly changes into the 

 Desmograptus structure with irregular and coalescing branches, a change 

 which indicates the development of Desmograptus from the typical, also 

 geologically older Dictyonema. 



Fig.30 Desmograptus intri- 

 cutiis sp. nov. Enlartjrmerit of 

 proximal portion showing transi- 

 tion from straight to undulating 

 branches in lower part. Deep kill. 

 .X5.25 



