GRAPTOLITES OF NEW YORK, PART 2 l6j 



the general dimensions (width of branches, distance of branches, etc.) and 

 the above mentioned more delicate portions of D. crassu m would seem 

 to differ not at all from D . h a m i 1 1 o n i a e . In general the branches of 

 D. crass um are however thicker and since they are in both equally 

 distant from each other (25 in 25 mm), the open intervals in D. crassu m 

 are considerably smaller. Also the dissepiments are as a rule, placed 

 considerably nearer together. 



Gurley has described in his manuscript three species of Dictyonemas 

 from the Onondaga limestone of Leroy, N. Y. [see D . megadictyon, 

 D. leroy ense and D. perradiatu mj. From all of these D . 

 crassu m is readily distinguished. It is less coarse than the first two 

 and coarser than the last one. 



Dictyonema leroyense Gurley ms 



Plate 3, figure 3 



Gurley's description is : 



Polypary arising from and sessile upon a discoid base which consists of 

 a carbonaceous film in which structure is evident but which, from the state 

 of preservation, cannot be more closely described than as consisting of a 

 number of minute elliptical pores about 0.3 mm long, 0.2 mm wide, and 

 about 0.2 mm apart (say 0.4, center to center). In addition the surface 

 seems to present a tendency to an apparently subregular mammillation, but 

 this is less certain. 



Polypary, in circularly compressed specimens, radiating somewhat 

 rapidly, in those compressed from the side not expanding so rapidly ; 10 mm 

 long, and 15 mm wide. Branches rather straight, subparallel, 17-20 in 

 25 mm, about 0.6 mm wide, judging from the few places where they are 

 satisfactorily exposed. Dissepiments of medium thickness, about 13-15 in 

 25 mm, usually straight and transverse. Meshes typically subquadrangular, 

 occasionally less regular. Thecae invisible. 



Horizon and locality. Two specimens in the National Museum from 

 the Corniferous limestone (Upper Helderberg formation), Leroy, N. Y. 

 Collector, Charles Schuchert. 



This species most nearly approaches D. megadictyon from the 

 same beds, but the branches are straighter, and both they and the dissepi- 

 ments are more numerous and more slender than in that species. The 

 structure of the base is — in so far as it can be made out — in exact accord 

 with that found in D. polymorphum of the Niagara. And this 

 agreement may perhaps furnish a valid basis for a generic distinction 



