OLENELLUS AND OTHER GENERA OF MESONACID^ 



257 



pleural lobes are all primitive characters indicating" a nearer approach 

 to an annelidian ancestor than any other form of the Mesonacidae. 



Ncvadia differs from EUiptoccphaki Emmons [pi. 24] in the more 

 primitive character of the eye lobe in the adult and in the character 

 of the posterior rudimentary segments. 



Ncvadia differs from Mesonacis Walcott [pi. 26] in the absence 

 of an enlarged third thoracic segment in the adult and in the char- 

 acter of the ten posterior rudimentary thoracic segments. 



NEVADIA WEEKSI, new species 



Plate 23, Figs. 1-7, Text Figs. 14 and 15 



Holmia wecksi Walcott, igo8, Smithsonian Misc. Coll., Vol. 53, No. 5, 

 p. 189. (Name given in list of fossils occurring in 12 of the section; 

 the species does not occur in 3, 6, or 11 of the same section, npr in 2J 

 of the Waucoba section [p. 187]. The specimens identified with this 

 species from 3 of the section are referred in this paper to IVanneria 

 gracile; those from 6 are referred to Olcnellus fremonti; those from 

 II are not specifically identified; and those from 2j of the Waucoba 

 section are referred to Olcnellus fremonti.) 



Fig. 15. 



Ncvadia zceeksi, new species. 



Fig. 14. Posterior portion of the dorsal sliicld preserving 18 rudimentary 

 segments and the pygidium. Locality No. if, south of Silver 

 Peak, Esmeralda County, Nevada. U. S. National Museum, 

 Catalogue No. 567921. 

 15. Anterior portion of dorsal shield associated with the specimen rep- 

 resented by fig. 14. U. S. National Museum, Catalogue No. 

 56792J. 



