1 68 NEW YORK STATE MUSEUM 



between these upper Paleozoic Dictyonemata and those of the Upper 

 Cambrian and Lower Ordovician. 



Dictyonema megadictyon Gurley ms 



Plate s, figure 5 



Gurley's description is : 



Polypary in the type specimen very stout, moderately radiate. Branches 

 subparallel, very thick, apparently not uniformly so, thickenings seeming to 

 take place especially just below the points of bifurcation ; about 0.8-1.0 mm 

 (0.6-1.2 mm the extreme limits; the great apparent range probably due to 

 imperfect exposure or flattening); only 12-14 in 25 mm. Dissepiments 

 very thick. One measured more than 1 mm wide, and being slightly oblique 

 gave the impression of branch fusion, as in Dcsmograptus. Dissepiments 

 often curved. Meshes usually quadrangular but sometimes less regular 

 being subrhomboidal or trapezoidal. 



Horizon and locality. Three specimens in National Museum from the 

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

 lector, Charles Schuchert. 



The great coarseness of the meshwork and branches is a distinctive 

 feature which separates it at a glance from most species of the genus. 



Dictyonema perradiatum Gurley ms 

 cf. D. fenestratum Hall 



Plate 4, figure 3 



Gurley's description of this form is : 



Polypary palmately radiating, the lateral branches retrocurved. Branches 

 30-32 in 25 mm of width, 0.4 mm thick, except a very few of the proximal 

 ones which reach 0.5 mm or occasionally even 0.6 mm. Corresponding to 

 the amount of radiation the branches in places arise not by dichotomy but 

 branch off more or less laterally as from a main stem. ' Meshes usually 

 about 1.-1.25 mm long. At the origin of the dissepiments the branches 

 sometimes bend slightly inward (toward the dissepiments), thus narrowing 

 the mesh and giving it a slightly elongated hexagonal form, and the branches 

 a slightly zigzag wavy appearance. Thecae about 60-65 m 2 5 mm. 



Horizon and locality. One specimen in the National Museum from 

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

 Collector, Charles Schuchert. 



This is a well marked species. Perhaps it resembles D. crass i- 

 b a s a 1 e (Gurley manuscript) as closely as any other species, but it lacks the 

 main distinctive characters of that species, not having the branches so undu- 

 late or so heavy, and having them more numerous in 25 mm of width. 

 Besides it is a more spreading form. 



