456 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



PTYCHOPARIA Corda. 



Ptychoparia penfieldi 11. sp. 

 PI. LXY, figs. 4, 4a, 6, 



Of this species there are in the collection the central parts of the head, 

 the interior of one free cheek, and one pygidium. The general form of the 

 head is transverse, semicircular; the frontal rim strong, rounded, and 

 separated from the frontal limb and free cheeks by a well-defined rounded 

 furrow; posterior lateral angles prolonged into slender spines. Glabella 

 truncato-conical ; nearly as broad at the base as long; marked by three 

 pairs of glabella furrows, which penetrate about one-fourth the distance 

 across ; the posterior pair bend slightly backward and penetrate toward the 

 center. Fixed cheeks narrow and separated from the glabella by a well- 

 defined dorsal furrow, from the narrow posterior rim by a rather broad, 

 clearly defined furrow ; anteriorly they merge into the rather narrow 

 frontal limb. Palpebral lobes narrow and clearlj'- defined by a groove from 

 the fixed cheek; they are nearly one-third the length of the cheek; ocular 

 ridges barely discernible above the general surface of the cheek. The 

 posterior lateral lobe of the fixed cheek extends outward, so as to give a 

 total length from the glabella outward somewhat greater than the width of 

 the glabella at the base. The associated free cheek has a strong marginal 

 rim and well-marked furrow between it and the main body of the cheek, 

 which reaches up to the palpebral lobe. 



Pygidium small, semicircular; axial lobe strongly defined and marked 

 by three segments and a short terminal portion; lateral lobes marked by 

 three rather broad segments that merge into the smooth outer rim. Surface 

 apparently smooth. 



Formation and locality: Middle Cambrian, Flathead terrane, Crow- 

 foot section, Granatin Range, Yellowstone National Park. 



Ptychoparia antiquata Salter sp. 

 PI. LXY, figs. 7, la. 

 Conocephalus antiquatus : Quart. Jour. Geol. Soc. London, Vol. XV, p. 554, fig. 2. 



This species was founded on an entire trilobite sent to the great exposi- 

 tion in London in 1851. It was said to have been discovered somewhere 



