24 



of the pygidium. In the Atractopygidce the pleurae of 

 the pygidium of A, verrucosus, have from 4 to 6 nodes 

 running down the centre of each pleurse, but the axis 

 is marked with 4 lateral rows of tubercles. 



Niagara Group : Eaton and Yellow Springs, Ohio ; 

 Medina, Orleans County, and Reynale's Basin, Niagara, 

 New York. 



Cryptonymus Nereus. Hall, 1867. 

 Encrinueus Nereus Hall, 20th. Eeg. Rep. N. Y. Cab. P. 375. 



"Pygidium triangular ; length and breadth about 

 equal. Axis sharply elevated and marked by about 18 

 rings, (well defined and extending across the axis) with 

 a further extension upon which no markings are dis- 

 tinguishable. The latteral lobes are marked with 8 or 

 9 pleurae, which in the cast are not tuberculated." 



Formation and locality : Niagara Group ; Racine, 

 Wis. 



The Encrinurus Trentonensis, Wal., may be a syno- 

 nym of this species, although Walcott's species has an 

 axis, in which the first anterior ring is marked with a 

 node on its centre, then in order the 3, 4, 10, 18 aijd 22 

 rings ; which gives these forms certain affinities with 

 the Encrinurus multisegmentatus, of which Nieszkowski 

 says : "The axis has not the smooth central space com- 

 mon in all other species of Encrinurus and generally 

 covered with tubercles ; very small nodes can be seen, 

 with a lens, on perfect specimens along the centre of 

 the axis of the pygidium. The number of pleurae is 

 generally nine, seldom ten." 



