DESCRIPTION OF GENERA AND SPECIES. 183 



Ptychaspis calchas Walcott. 

 Plate 16, Figures 13, 130. 



Ptychaspis calchas WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 71. (Described as a new 

 species essentially as below.) 



Of this species only more or less imperfect specimens of the central portions of 

 the cephalon, exclusive of the free cheeks, are known. Glabella slightly convex on 

 the posterior half and moderately convex at the frontal lobe; it is divided by two 

 transverse, rather strong, shallow furrows into two narrow lobes that arch slightly 

 backward, and an anterior lobe that measures a little more than half the length of 

 the glabella ; a pair of very slightly impressed and short furrows marks the side of 

 the frontal lobe a little back of the center ; occipital furrow broad, shallow, and about 

 the same strength as the two furrows crossing the glabella ; occipital ring narrow at 

 the sides, increasing in width toward the center, where it rises at the back above the 

 general level of the glabella; dorsal furrow broad and rounded. 



Fixed cheeks scarcely more than a very narrow ridge rising from the broad dor- 

 sal furrow to the palpebral lobe and sloping gently backward into the postero-lateral 

 limb and forward, in front of the palpebral lobe, into the frontal border of the 

 cephalon; palpebral lobe about one-fourth the length of the cephalon and marked 

 by a strong furrow within the narrow rim ; frontal rim nearly flat, of medium width, 

 and sloping forward and downward from the dorsal furrow to the frontal margin; 

 postero-lateral limb about as long as the width of the glabella, and marked by a 

 broad, shallow furrow within the narrow posterior margin. 



The cast of the interior surface of the test appears to be minutely punctate 

 under a strong lens, and fragments of the exterior appear to be smooth. 



The largest specimen of the cephalon in the collection has a length of about 

 22 mm.; a specimen i mm. in length has a glabella 5 mm. in width, with a fixed 

 cheek a little less than 2 mm. in width from the sides of the glabella across the dorsal 

 furrow to the furrow on the palpebral lobe. 



This species differs from the described species of the genus in the low convexity 

 of the glabella, the uniformity of the occipital and two posterior furrows of the 

 glabella, and the apparently smooth surface. 



Formation and Locality. Upper Cambrian: (C41) Lower part of the Ch'au- 

 mi-tien limestone [Blackwelder, 19070, p. 36 (part of the first list of fossils)], 2.7 

 miles (4.3 km.) southwest of Ch'au-mi-tien, Shan-tung, China. 



Collected by Eliot Blackwelder. 



Ptychaspis callisto Walcott. 

 Plate 16, Figures 14, 140. 



Ptychaspis callisto WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxix.p. 72. (Described as a new species 

 essentially as below.) 



Of this species only the central portions of the cephalon exclusive of the free 

 cheeks, are known. Glabella moderately convex, and divided into a narrow pos- 

 terior lobe by a broad, rounded, deep transverse furrow that curves slightly back- 

 ward, and an anterior lobe, about as long as wide, marked upon its lateral slopes by 

 two pairs of short, narrow furrows; it is broadly rounded, almost transverse in 

 front, and its sides are subparallel ; occipital furrow broad and deep, and arching 

 slightly forward at the center; occipital ring narrow at the ends, widening and rising 

 gradually toward the center, which appears to have been elevated above the general 

 surface of the cephalon; dorsal furrows strong and deep. 



