DESCRIPTION OF GENERA AND SPECIES. 127 



ring ; two obscure ridges run down the posterior slope of the central axis from the two 

 nodes upon the posterior end of the central axis and terminate in spines on the 

 border; each of the rings of the pleural lobe, including the anterior border, terminates 

 in a long, slender spine, that of the anterior border being much longer than the 

 others; this arrangement gives five spines on each side of the axis and two spines 

 back of the axis ; the border is rounded and much interrupted by the strong spines 

 extending out from it. 



Surface of the crust minutely punctate under a strong lens, and marked by 

 strong pustules, more or less irregularly arranged on the surface, except in the fur- 

 rows ; on the segments of the thorax the pustules are arranged on the front and back 

 margins of the pleurae and on the higher portions of the rings on the axis; on the 

 pygidium the pustules occur on the elevated rings and somewhat irregularly on the 

 pleural lobes, but not on the spines. On some portions of the surface, under a very 

 strong lens, there appears to be an irregular, inosculating, elevated series of lines or 

 striae interrupting the surface, leaving minute depressions or punctae between them. 



The portion of the thorax preserving twelve segments has a length of 50 mm., 

 with a width at the anterior end of the axis of 16 mm., and on the pleural lobes of 24 

 mm. ; the cephalon of this specimen has a length of 26 mm. and a width of 64 mm., 

 exclusive of the postero-lateral spines. 



The pygidium of this species is not unlike that of Blackwelderia sinensis (Ber- 

 geron) [p. 121], but it differs in the more depressed axis and in the character of the 

 spines on the border. This conclusion is given after an examination of the figures 

 of M. Bergeron a.nd a comparison of specimens which have been identified from the 

 Ku-shan shale formation, 2.5 miles (4 km.) southwest of Yen-chuang, Sin-t'ai-hien, 

 Shan-tung, China, which appears to be the horizon from which the various species 

 described byM. Bergeron were obtained. From Olenoides marcom Whitfield [Wal- 

 cott, 18910, plate 94, figs. 2, 2a-b] the pygidium of Damesella blackwelderi differs in the 

 same manner as from Blackwelderia sinensis. From Dorypyge slatkowskii Schmidt 

 [1886, p. 418, plate 12, figs. 11-14] it differs in the character of the cephalon and the 

 general shape of the pygidium and its spinose border. From Blackwelderia alastor it 

 differs in the slender axis and spinose border of the pygidium. 



This is one of the finest of the trilobites collected by Mr. Blackwelder; and 

 owing to the fact that there are a number of specimens of the head and pygidium, 

 and one specimen preserving the head attached to twelve segments of the thorax, it 

 was possible to separate it from the genera Dorypyge and Olenoides and to establish 

 a new generic type. 



Formation and Locality. Middle Cambrian : (0 12) Gray limestone near the 

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

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

 southwest of Yen-chuang: (013) yellow slabby limestone in the middle limestone 

 member of the Kiu-lung group [idem (part of first list of fossils)], on the west slope of 

 hill in angle between two faults, just east of the granite mass of the Lien-hua-shan, 6 

 miles (9.6 km.) southwest of Yen-chuang; (014) in talus from the middle limestone 

 member of the Kiu-lung group [idem, p. 37], 2.8 miles (4.5 km.) southwest of Yen- 

 chuang; and (040), limestone nodules in green shales in the middle limestone mem- 

 ber of the Kiu-lung group [idem, pp. 37 and 41 (part of the first list of fossils)], in a 

 gully in bank of river 2 miles (3.2 km.) south of Yen-chuang, Sin-t'ai district, 

 Shan-tung, China. 



Collected by Eliot Blackwelder, Bailey Willis, and Li San. 



Also from (36 f) Fu-chou series, about i ,000 feet (305 m.) above the white quartz- 

 ite [see Blackwelder, 19076, p. 92, for general stratigraphic relations], collected in a 



