DESCRIPTION OF GENERA AND SPECIES. 185 



strongly convex in front, but not at all globose or tumid; it is broadly rounded, 

 almost transverse in front, and has parallel sides; frontal limb very narrow in front 

 of the glabella, widening at the sides; it is separated from a downward-sloping 

 frontal rim by a very narrow transverse furrow; the frontal rim is very slightly 

 convex, and from two to three times as wide as the frontal limb in front of the 

 glabella ; dorsal furrow narrow and deep on the sides, and little more than a line in 

 front of the glabella. 



Fixed cheeks very narrow at the front and back and merging into a large pal- 

 pebral lobe at the center; they rise rapidly from the dorsal furrow and arch over 

 into the furrow within the narrow palpebral lobe; palpebral lobe extends from 

 opposite the anterior pair of furrows on the frontal lobe of the glabella back to the 

 posterior transverse furrow. 



Surface marked by large, low, closely arranged granulation or pustules. 



This is a small species, the type specimen of the glabella having a length of 

 only 4 mm., with a width of 2 mm. 



Formation and Locality Upper Cambrian: (C42) In the central part of the 

 Ch'au-mi-tien limestone [Blackwelder, 19070, p. 36 (second list of fossils)], 1.8 miles 

 (2.9 km.) west-southwest from the temple on Tsing-lung-shan, 7.5 miles (12 km.) 

 east of Ch'au-mi-tien, v Shan-tung, China. 



Collected by Bailey Willis. 



Ptychaspis ceto Walcott. 

 Plate 1 6, Figures 17, ija-d. 



Ptychaspis ceto WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 73. (Described and discussed as 

 a new species essentially as below.) 



Cephalon, exclusive of the free cheeks, subrhomboidal in outline, strongly 

 convex. Glabella large, strong, with very convex frontal lobe, sides subparallel, 

 front broadly rounded ; two strong glabellar furrows cross transversely from side to 

 side, dividing the glabella into two rather narrow posterior lobes and an anterior 

 globose lobe that slightly overhangs the frontal rim; occipital furrow about as 

 strong as the two glabellar furrows ; occipital ring narrow and slightly rounded, and 

 elevated at the center; dorsal furrows strong and deep on the sides and in front of 

 the glabella. 



Fixed cheeks with the dorsal furrow about two-thirds the width of the glabella, 

 the fixed cheeks forming an elevated ridge at the palpebral lobe, with an elevated, 

 short ridge opposite the anterior end of the palpebral lobe, that is crossed by three 

 transverse ridges, as seen in the cast of the inner surface; in front of the elevated 

 portion the cheek drops gently to the frontal rim; back of the palpebral lobe the 

 cheek slopes gently and merges into the postero-lateral limb ; palpebral lobe narrow, 

 elongate, a little more than one-half the length of the cephalon, and separated from 

 the fixed cheek by a narrow, deep furrow; postero-lateral limb about as long as the 

 width of the glabella at the base, and marked by a broad, deep, rounded groove, 

 within the sharp, elevated posterior margin; frontal limb very short and sloping 

 downward into the rounded frontal rim; the frontal limb and rim form scarcely 

 more than the outer border of the strong dorsal furrow. 



Outer surface unknown, as in all the specimens the test clings to the matrix; 

 this latter fact indicates that it was roughened, probably tuberculose. The cast of 

 the frontal lobe of the glabella shows a number of irregular, concentric ridges and 

 grooves subparallel to the frontal margin. 



The largest cephalon in the collection has a length of 14 mm., with a width at 



