194 NEW YORK STATE MUSEUM 



cus) and e. g. a Dictyonema consists in the fact that here the individuals 

 are kept together for some time in order to empty afterwards in alternating 

 groups." 



In our form [see pi. 7, fig. 4] the branchlets are distinctly composed of 

 a greater number of individuals (5-10) whose apertures become visible in 

 somewhat weathered specimens. There may hence exist a still wider varia- 

 tion in the number of individuals emptying on the branchlets than Wiman 

 found between his two species. 



Pocta has placed only forms with distinct "scales" under Inocaulis and 

 by this safe proceeding excluded forms resembling Palaeodictyota 

 anastomotica which have the general appearance of an Inocaulis but 

 lack the projecting groups of individuals. But his forms are also more 

 properly referred to Acanthograptus. 



He distinguishes in the compressed material two sizes and forms of 

 "scales" or lamellae, (1) very fine, scaly, closely arranged lamellae and (2) 

 larger spiniform extensions, being placed on each side in alternating rows. 

 The former are the individuals in the branches which in the compressed 

 specimens produce by their divergence a characteristic scaly effect ; and the 

 latter the branchlets consisting of the emptying individuals. 



Acanthograptus walkeri (Spencer) 



Plate 6, figures i, 2 ; plate 7, figure 4 



Inocaulis walkeri Spencer. Can. Nat. 1882. 10:165 (nomen nudum) 

 Inocaulis walkeri Spencer. Acad. Sci. St Louis. Trans. 1884. 4:564,585,586; 



pl- 5, fi g- 2 

 Inocaulis walkeri Spencer. Mus. Univ. State Mo. Bui. 1884. 1:14, 31,36; pl. 5, 



fig. 2 

 Inocaulis walkeri Gurley. Jour. Geol. 1896. 4:99,309 



The Rochester shale at Middleport, N. Y. has afforded four well 

 preserved specimens of a form which by comparison with material of the 

 Spencer collection from the Niagaran at Hamilton, Ontario, we have 

 identified with this species. 



Spencer's diagnosis is very brief and Gurley lias care-fully redescribed 



