300 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



Fovhiiition and locality. — Middle ? Cambrian, Coarse grained, some- 

 what friable, glauconitic sandstone. Drift bowlder No. 3 on Egge- 

 grund Island, North Baltic region, Sweden. 



For note on the geological horizon se(^ description of O. ( Westonia) 



bottnlaa. 



ACROTRETA EMMONSI, new species. 



Only the interiors of the two valves are known of this species. One 

 of them shows the distinct character of the vascular markings and 

 muscle scars. The only shell with which it can be compared is the 

 dorsal valve of Acrotreta idahoensis. At first sight I was inclined to 

 refei' this shell to Oholella, but its corneous test, cardinal muscle scars, 

 and absence of area of the Oholella tj^pe, prevented. Fragments of 

 Olendlax occur in the layer of limestone from which the specimens 

 were obtained. 



The specific name is given in memory of Dr. Ebenezer Emmons, 

 who studied and wrote of the Bald Mountain section. 



Formation and locality.- — Lower Cambrian. Limestone interbedded 

 in shales on upper part of the west slope of Bald Mountain, township 

 of Greenwich, Washington County, New York, 



ACROTRETA LIANI, new species. 



Shell small, about 1.5 nun, in diameter; outline of aperature sub- 

 circular, the posterior side being- slightly transverse. Ventral valve 

 conical with the apex a little in advance of the posterior margin; 

 false area indefinite, except for a rather strong, flat furrow that 

 extends from the apex to the margin; the elevation of the valve is 

 about two-thirds its diameter at its aperature. Dorsal valve slightly 

 convex, apex marginal. Surface of shell marked by fine, concentric 

 striie and lines of growth that on the dorsal valve tend to form low 

 ridges toward the outer margins. 



Observations. — This species is the representative of the American 

 Acrotreta idahoensis sulcata. It has the same type of false area, and 

 the ventral valve is of average height. The specific name is given in 

 recognition of Lian, Mr. Willis's faithful Chinese interpreter. 



Formation and locality. — Middle Cambrian. Chang Hsia limestone 

 in upper oolitic portion, Chang Hsia, Shantung, China. 



Collections of Mr. Eliot Blackwelder, Carnegie Institution of Wash- 

 ington, expedition to China. 



ACROTRETA NEBOENSIS, new species. 



This is one of the Acrotrda. idahoensis forms of the genus. The 

 ventral valve is moderately elevated, the apex projecting slightly over 

 the nearly vertical false area. The latter is marked midway by a very 

 nari'ow false pedicle furrow. 



