I08 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



Formation and locality. — Ozarkian : (6iq) Chushina formation. 

 Gray limestone in beds of varying thickness one or two layers quite 

 ferruginous. In Billings Butte (Extinguisher), at end of west spur 

 of Mt. Lynx, above Hunga Glacier -and east of Robson Peak, Robson 

 Park, northwest of Yellowhead Pass, in eastern British Columbia, 

 Canada. 



SYMPHYSURINA Ulrich 



Symphysurina Ulrich in Walcott, 1924, Smithsonian Misc. Coll., Vol. 75, 

 No. I, p. 27- 



Quotation from Dr. Ulrich's manuscript : 



Description. — '' Cephalon strongly convex, a quarter-sphere in 

 form. Cranidium subquadrate, usually longer than wide, excepting 

 the more or less produced post-lateral extremities, bordered in front 

 with a narrow striated rim. Palpebral lobes situated either midway 

 between the anterior and posterior angles or somewhat behind the 

 midlength of the cranidium, the length of the lobes equaling one-sixth 

 to one-fourth the length of the cranidium, and between one-fourth 

 and one-third the distance between their bases. Eyes moderate in size 

 and prominence, facetted as in the Asaphidae. Median tubercle small 

 but constantly present, situated between the eyes, hence far from the 

 posterior edge. Glabella large, unfurrowed, convex, not defined in 

 front of the eyes and usually but faintly outlined behind them ; 

 fixed cheeks narrow. Neck furrows and neck ring practically indis- 

 tinguishable. Sutures nearly straight and commonly diverging slightly 

 anteriorly from the eyes, reaching the edge of the cephalon which 

 they follow in passing around the front of the cranidium. Free cheeks 

 large, rounded triangular to subquadrate in outline, the posterior 

 edge curving forward to the genal angle which is broadly obtuse, 

 sharply pointed, or drawn out into a spine. Surface of cheeks with 

 or without a wide, undefined, depressed border, and more generally a 

 striated raised rim that increases in prominence as it approaches the 

 anterior angle of the cranidium. This rim is the dorsal edge of the 

 doublure which continues its course beneath the front edge of the 

 cranidium until it meets the similar extension from the opposite cheek. 



" The associated hypostoma is broadly alate anteriorly, with a 

 deep pit at the middle of the anterior edge making this part appear 

 bilobed, median portion strongly swollen; posterior margin rounded, 

 with two concentric, partly interrupted ridges. The marginal ridge 

 dies out forward on the posterior part of the anterior wings. 



" Thorax known only from fragments of the segments ; the axis 

 approximately one-third the width. An imperfect specimen suggests 



