Mc Learn —Silurian Arisauj Series of Arisaiy, N. 8. 137 



the interpretation to evidence based on the other groups 

 is for the purpose of eliminating', as far as possible, this 

 ecological factor. 



New genera and subgenera. 

 It is proposed below to present a brief description of 

 the new genera and subgenera, Where the genotypes 

 are new species, they are also described. The final 

 report will include the taxonomy of the entire fauna of 

 169 species and varieties. 



Class Brachiopoda Dumeril. 



Family Rhynchonellidse Gray. 



Genus Camarotoechia Hall and Clarke. 



Pectorhyncha, new subgenus. 



(II?7«:to9, fixed.) 



Obtusely plicated Camarotoechia in which the teeth are 

 not supported freely by dental plates extending into the 

 valves, but are cemented to the lateral walls of the ventral 

 valve. Resembles Pletliorhyncha Hall and Clarke in the 

 prominently elevated and posteriorly thickened dorsal 

 median septum and the thickened hinge-plate and crura. 

 Lacks the fine median sulcus on the anterior part of the 

 plications which is present in Wilsonia, Pletliorhyncha 

 and Uncinulus. Divided hinge-plate and crural cavity 

 as in Camarota'chia. 



Genotype: Atrypa obtusiplicata Hall. 



Genus Eatonia Hall. 

 Pareatonia, new subgenus. 



1857 Eatonia Hall (partim), 10th Eept. N. Y. State Cab. Nat. Hist., p. 90. 



This subgenus is erected to embrace the plicate 

 Eatonia stock of E. medialis (Vanuxem), E. sinuata Hall, 

 etc. Eatonia is restricted to those forms which are 

 finely striate but not plicate. They may be crenulate at 

 the margins, however, "as if by the extremities of the 

 rounded plications" (Hall and Clarke 1894, p. 206). 



Genotype: Eatonia medialis (Vanuxem). 



Eatonioides, new genus. 

 (Eatonia A- et'So?, form.) 



The exterior of these forms is similar to that of the 

 plicate or Pareatonia species of Eatonia. The broad, 



