Vol. 1. Sun — Cambrian Faunas of North China (iv) 73 



Associated with these is a large number of free cheeks and genal spines which apparently 

 belong to this species. 



"Glabella large, almost parallel-sides except for the slightly wider snbglobose 

 anterior lobe, which is strongly convex and but slightly wider transversely, its antero- 

 posterior dimension somewhat less than half the length of the entire glabella. Anterior 

 glabellar furrow complete slightly less pronounced in the center and very gently arcuate; 

 second furrow more strongly deflected backwards and faint in the center; occipital furrow 

 similar to the anterior furrow but broader at the sides and somewhat fainter in the center; 

 the convexity of the posterior segments somewhat less than that of the anterior lobe. Oc- 

 cipital segment slightly broader than second and third segments which are of equal width. 



"Fixed cheeks flat or very gently convex; their width somewhat more than 

 half the width of the glabella, broadly grooved posteriorly by the lateral extension of the 

 occipital furrow. 



"The associated fi-ee cheeks are large and extended into a long gently curved 

 genal spine. The outer contour is gently and regularly convex, and the inner side 

 contracts rapidly to the very gently tapering genal spine, which has a subcircular or 

 broadly ovoid section with the narrow end on the inside. It is marked by subequally 

 spaced, rather distint and more or less continuous longitudinal strise. The length of the 

 genal spine is considerable, being much greater than that of the glabella; its terminal 

 end tapers rather more rapidly. 



"Surface apparently smooth, though in one specimen there is a suggestion of 

 faint discontinuous and concentrically placed wrinkles on the anterior lobe of the 

 glabella. 



"The specimens occur in a limestone conglomerate (intraformational) with large 

 worn limestone pebbles. The slender genal spines are by far the most numerous, and 

 they are mostly fragmentary, the anterior expansion of the free cheek being shown only 

 in a few specimens. They are very like the genal spines of some species of Paradoxides, 

 but more curved, and they are longer and more slender than those of any other species 

 of Ptychaspis from the Cambrian of China, They are also much longer proportionately, 

 more cylindrical and less rapidly - tapering than are those of P. minicaensis Owen, the 

 type species of the genus, from the St, Croix beds of Wisconsin. 



"This species approaches Ptychaspis calyce Walcott, from the Upper Cambrian 

 Ch'aumitien limestone of Shantung, in the form of the glabella but the anterior lobe is 

 longer more nearly subglobose while the second furrow is more deflected backwards 



