302 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



valve has a strong median ridge extending from the posterior margin 

 two-thirds the distance toward the front. A small elev^ated cardinal 

 scar occurs on each side of the median ridge a little in advance of the 

 posterior margin. Main vascular sinuses rather strong; they start 

 beneath the apex and extend forward a short distance from the outer 

 lateral margin of the shell. Surface marked V)v hue concentric striae 

 and lines of growth. 



Ohservations, — This shell in size and general form is closely related 

 to Acrotreta rat cvo.hco pica of the Middle Cambrian fauna of the United 

 States. It occurs quite abundantly in a chocolate-colored limestone 

 associated with Oholnn {Llngnlella) rhlnriiHis. 



Fonnation and locality. — Middle Cambrian. Chang Hsia limestone. 

 Yen Chuang and 2^ miles south of Yen Chuang, Shantung, China. 



A shell apparently identical with ^1. !^hantungens!s was collected 

 from a line-grained ])luish-black limestone river drift block 1 mile 

 south of Chen Ping Hsien, on the Lan Ho River. 



Collections of Mr. Bailey Willis and Mr. Eliot Blackwelder, Carnegie 

 Institution of Washington, expedition to China. 



ACROTRETA SPINOSA, new species. 



The general form of this shell is much like that of Acrotreta idaho- 

 ohsin. It differs in having a straighter posterior margin. The main 

 character of the species is the spinose outer surface. The surface is 

 marked by tine concentric lines of growth at irregular intervals, with 

 numerous, very tine, thread-like stria3 between. On some shells 

 radiating, more or less irregular, tine, rounded ridges occur that are 

 formed by the elevated elongate spine bases. When these elongate 

 bases are irregularly arranged, the radiating ridges are not present. 

 Owing to their minute size the spinules are rarely seen. 



Formation and locaUii/. — Upper Cambrian, Hamburgh shale. Ham- 

 burgh Ridge; east side of Sierra Canyon opposite Pinnacle Peak and 

 also opposite the Jackson Mine, Eureka District. Nevada. 



ACROTRETA UPLANDENSIS Wiman. 



Acrotreta Hplandensig Wimas, Bull. Geol. Institute, Upsala, No. 2, YI, 1903- 

 Pt. 1 ; Studien Nordbaltische Silurgebiet, p. 54, pi. ii. figs. 15-18. 



This species recalls at once A. idaJioensis sulcata. It differs from 

 it in having a broader false area. The surface is marked b}^ tine 

 thread-like stria? that cross the false area and false pedicle groove. 



Formation and localitii. — Middle ? Cambrian. Gray bituminous 

 sandstone in drift bowlder No. 2 on Biludden Island. Also in glau- 

 conitic sandstone, bowlder No. 1, at Hoganas Commune of Borstil, 

 Sweden. 



