1 64 



NEW YORK STATE MUSEUM 



branches down to the root, which may be considered as additional diag- 

 nostic characters of the genus, find their strictest expression in C. cyathi- 

 f ormis, the form which is cited as the genotype by Miller [X. Am. Geol. 

 & Pal. 1889, p. 1 75]. 



As both Spencer's drawings and our material show, these characters 

 are not retained in his second species, C . subretif ormis. The latter 

 clearly possesses dissepiments which however are so oblique, that they 

 appear as bifurcations [see Spencer's figure, here copied]. Dictyonema 

 polymorph um Gurley indicates the transition from a typical Dicty- 

 onema with rectangular meshes to this irregularly meshed form. The 

 clearly closer relationship of the present species to Dictyonema poly- 

 morphum than to C. cyath if ormis has induced us to place it 

 under the former genus and to restrict Calyptograptus to forms which retain 

 the diagnostic characters of the genotype. 



Dictyonema areyi Gurley ms 



Plate 4, figure 2 



Dr Gurley describes this form as follows : 



Polypary arising from a bulbous base, 

 cyathiform, hardly at all radiate, the sides 

 subparallel above. Branches 0.6 mm wide, 

 and 30 in a width of 25 mm; dissepiments 

 very heavy (some reaching 0.6 mm), con- 

 cave-sided, 25 in 25 mm. But they may be 

 (often are) much narrower either from wear- 

 ing or from the shale not splitting accu- 

 rately in their plane. Meshes rounded- 

 oblong, or elliptic. Thecae invisible. 



Horizon and locality. Niagara shale, 

 Rochester, N. Y. Four specimens (includ- 

 ing the types) in collection of Prof. A. L. 

 Arey, Rochester, N. Y., to whom the 

 species is dedicated. 

 Hen mctyonema are,-; Guriey m S . This species is about the most distinct 



Enlargement (x 5) of basal portion of type specimen Q £ ^ g enus> hardly rCSCml)ling UllV Other. 



The specimens consist only of flattened blacker films on the black shale. 

 But the great thickness of the dissepiments, their biconcave-sided character 

 and the consequent rounded oblong, or oval meshes, easily characterize the 

 species. 



