NO. 5 CAMBRIAN TRILOBITES RESSER 29 



Pygidium flat. Axis defined by shallow dorsal furrow, but chiefly 

 by arching above pleural lobes ; extends to border. Pleural furrows 

 faintly outlined. Border flattened. 



Genotype. — Ptychoparia lacviccps Walcott. 



Range. — IVIiddle Cambrian. 



Name. — E repose: another ; ao-7ris = shield. 



Eteraspis laeviceps (Walcott) 

 Ptychoparia lacviccps Walcott, U. S. Geol. Surv. Monogr. 8, p. 54, pi. 10, 

 fig. 17, 1884. (Not 18 ^^ Ehinania oivcni?.) 



Middle Cambrian, Eldorado; (loc. 58) east side Secret Canyon, 

 Eureka District, Nevada. 



Holotype and parafypes. — U.S.N.M. no. 24614. 



GLOSSOPLEURA Poulsen, 1927 

 Glossoplcura Poulsen, Meddels. Gr^nland, vol. 70, p. 268, 1927. 



Diagnosis. — Cephalon and pygidium large, of about equal size. 

 Glabella wide, extending to anterior margin, where a narrow upturned 

 brim may sometimes be present ; glabella sometimes expands some- 

 what forward of the eyes ; four faint pairs of glabellar furrows usually 

 traceable. Fixed cheeks small ; eyes large, situated well back. Free 

 cheeks rather wide with a broad rim when the wide doublure is im- 

 pressed on them, otherwise sloping smoothly to margin. 



Thorax has seven segments. 



Pygidium usually has the axis well defined. Axial furrows often 

 faint ; pleural furrows faint but clearly traceable in some species to 

 outer edge ; wide rim sometimes definite, when doublure is impressed 

 on test. 



Genotype. — Dolichonictopus boccar Walcott. 



Comparisons.- — Glossoplcura, as pointed out by Poulsen, resembles 

 Anorla in the number of thoracic segments and the extension of the 

 glabella to the front margin, but difl:'ers in having longer eyes. How- 

 ever, his observation that Glossoplcura lacks the macropleural de- 

 velopment of the fifth thoracic segment does not hold if the present 

 specific references are all correct. 



From the other members of the family Glossoplcura it is distinguish- 

 able by its less developed furrows, the absence of a brim on the 

 cephalon, and the large size and posterior position of the eyes. 



Range. — Apparently confined to the Middle Cambrian of Green- 

 land, the Appalachians, and the Rocky Mountains. Frequently the 

 species of this genus constitute the entire fauna, except that an 

 Alokistocare may go with it. 



