380 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



segment from the central axis out to its blunt termination at the end 

 of the segment. 



Pygidium large, border very narrow ; axial lobe convex, about two- 

 thirds the length of the pygidium, and divided into seven rings and a 

 terminal section ; the rings are similar to those of the axial lobe of 

 the thorax and have a similar band and central tubercle ; the pleural 

 lobes are broad and marked by eight broad, shallow furrows and a 

 posterior pair that appear to come out of the posterior section of the 

 axis; each broad furrow is separated from those adjoining by two 

 narrow, sharp ridges with a narrow furrow between them that repre- 

 sents the anchylosed line of separation of the original segmentation 

 now united to form the pygidium. 



Surface minutely granular; the venation on the free cheeks and 

 the lines on the axial lobe of the thorax and pygidium have been 

 characterized above. 



Genotype. — Orria elegans Walcott. 



Dimensions. — The largest dorsal shield of the genus as now known 

 has a length of 7 cm. A large pygidium indicates that the individual 

 to which it belonged was at least 9 cm. in length. 



Stratigraphic and geographic range. — The one known species 

 occurs in the Middle Cambrian Marjum formation in western Utah. 



Observations. — Orria is an OgygopsisASko. form that differs from 

 the latter in several marked characters. 



1. The cephalon is smaller in proportion to the thorax and 

 pygidium. (a) Fixed cheeks nearly absent between palpebral lobes 

 and glabella ; (b) palpebral lobes large and close to glabella ; postero- 

 lateral limbs long and narrow ; antero-lateral limbs only a narrow 

 space between the gabella and facial sutures ; facial sutures accord 

 with differences in fixed cheeks and limbs. 



2. Pleural furrows of thoracic segments broad and straight instead 

 of narrow and diagonal. 



3. Median axis about two-thirds the length of the pygidium. 



The relation of Orria to other genera of the Ogygiocarinse is not 

 any nearer than to Ogygopsis. Its relatively smaller cephalon, large 

 palpebral lobes, and narrow fixed cheeks suggest Ogygiocaris buchii 

 (Brongniart), but the pleural furrows and axial lobe of pygidium are 

 quite distinct. 



The resemblance between the cephalon of Orria and Bathyuriscus 

 (pi. 46) indicates that they originated from a similar ancestral type. 

 Both Orria and Ogygopsis suggest a stage of development between 

 Bathyuriscus and Ogygiocaris. 



