THE OTTAWA NATURALIST 



VOL. XXIX. JUNE-JULY, 1915 Nos. 3 and 4 



ON THE VALIDITY OF THE GENUS PLETHOPELTIS. 



(Raymond). 



By Richard M. Field. 



While studying some fossils collected by Dr. Percy E. Ray- 

 mond from the Hoyt Quarry, Saratoga, the writer became 

 interested in the relationship of the two forms which have been 

 described by Walcott as Agraulos saratogensis. In his recent 

 description (7) of the Hoyt fauna Dr. Walcott has figured a 

 form with strongly outlined glabella, bearing glabeilar furrows, 

 while in his first description of the fauna he illustrated under 

 this name a specimen with smooth glabella and very faint circum- 

 glabellar furrow. This latter, or " smooth-glabella " variety, is 

 found to predominate in the collection. A still closer inspec- 

 tion of the material seemed to show that although both forms 

 may belong to the same species, it is extremely doubtful if they 

 are to be placed under the genus Agraulos. The writer believes 

 that the following evidence shows that Raymond was justified 

 in erecting his new genus Plethopeltis for trilobites such as 

 Agraulos saratogensis Walcott. 



To determine the validit}^ of the genus Plethopeltis it is 

 necessar}^ to discuss the following facts. Raymond, in the 

 "Revision of the Bathyuridae" (8) designated Agraulos sara- 

 togensis instead of Bathyurtis armaius Billings, as the type of 

 the new genus Plethopeltis. It is tmdertsood that he did this 

 because only a single cranidium of P. armatus was known and 

 no pygidium, while numbers of pygidia were found associated 

 with P. saratogensis. Some doubt has recently been expressed 

 as to whether after all the species saratogensis should be removed 

 from the genus Agraulos. If the latter be the case, then the 

 genus Plethopeltis automatically drops out of the nomenclature. 

 Ra3^mond's generic diagnosis of Plethopeltis is as follows : — 



"Cephalon strongly convex, wider than long, without con-, 

 cave border or marginal rim. Glabella faintly defined, without 

 glabellar furrows. Eyes small, situated well forward. Free 



