DESCRIPTION OF GENERA AND SPECIES. 119 



This species differs from Damesclla blackwelderi [plate 10, figs, i, la-f] in 

 having a broader and more tapering glabella, a thin frontal rim, and a narrow frontal 

 limb. The pygidium referred to B. alastor has a more slender axis, flatter border, 

 two spines fewer on the margin, and two of the posterior spines of greater length. 

 The cephalon of B. alastor is much like that of Teinistion typicalis [plate 9, figs. 2, 

 2a-c], but it differs in the character of the frontal rim and the associated pygidium. 

 Teinistion alcon [plate 9, fig. 3] has a much broader fixed cheek and a different 

 frontal rim. 



It is difficult to make a satisfactory generic reference of this species, as it has 

 characters of both Blacku'elderia and Teinistion. It is referred to the former genus 

 on account of the associated pygidium. 



Formation and Locality. Middle Cambrian: (C12) Gray limestone near the 

 top of the middle limestone member of the Kiu-lung group [Blackwelder, 19070, 

 pp. 37 and 41 (part of the first list), and fig. 10 (bed 7), p. 38], 3.25 miles (5.2 km.) 

 southwest of Yen-chuang, Sin-t'ai district, Shan-tung, China. 



Collected by Eliot Blackwelder and Li San. 



Blackwelderia cilix (Walcott). 

 Plate 9, Figures 6, 6a-r. 



Olenoides (?) cilix WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxix, p. 27. (Described and discussed 



as a new species.) 

 Blackwelderia cilix (WALCOTT), 1906, idem, vol. xxx, p. 573. (Description of species extended and 



more thoroughly discussed.) 



This species is represented by numerous specimens of the central portions of 

 the cephalon, separated free cheeks, and associated specimens of the pygidium. 



These indicate that the general form of the cephalon was transversely semi- 

 circular and rather strongly convex, and that the margin of the cephalon was of 

 medium width in front, gradually widening to the free cheek, where it narrows 

 toward the base of the postero-lateral spine. A postero-lateral spine projects 

 backward and slightly upward from a point on the margin a little in advance of 

 the postero-lateral angle. Glabella truncato-conical in outline, and marked by 

 three pairs of furrows, the posterior of which extends obliquely backward nearly 

 to the occipital furrow; the anterior furrows are indicated by short, slight depres- 

 sions on the edges of the glabella next to the dorsal furrow; they are situated so 

 as to divide the space between the posterior furrows and the front margin of the 

 glabella into subequal spaces; a very narrow, slightly indicated, median, longi- 

 tudinal ridge extends from the occipital furrow nearly to the front of the glabella ; 

 occipital furrow strongly marked, rounded, and about as wide as the occipital 

 segment; occipital segment of medium width, convex, and arching forward slightly 

 at the center; a shallow furrow crosses it on each side so as to outline a rounded 

 node at each end; dorsal furrow rounded, rather strong at the ends, and merging into 

 the broad, concave slope of the frontal limb. 



Fixed cheeks about one-half the width of the glabella ; they rise abruptly from 

 the dorsal furrow to the base of the palpebral lobes and slope rapidly from the pal- 

 pebral lobes backward to the posterior furrow and more rapidly to the front, where 

 they merge into the concave frontal limb; palpebral lobes small, elevated, separated 

 from the fixed cheeks by a shallow furrow, and situated opposite the central part 

 of the cephalon ; palpebral ridges indicated by depressed lines that extend from the 

 anterior end of the palpebral lobe, across the fixed cheeks, to the dorsal furrow; 

 postero-lateral limb about one-third the width of the cephalon within the facial 

 sutures; it is marked by a broad, shallow furrow within the narrow posterior 



