DESCRIPTION OF GENERA AND SPECIES. 75 



The data for comparison of this species with described species from America 

 and Europe are too limited to be of value. A comparison with Acrothele (Red- 

 lichella) granulata (Redlich) 1 Walcott [19126, p. 633, plate LVI, figs. 2, za-n], of the 

 Salt Range, India, shows a strong similarity in the interiors of the dorsal valves; 

 but I do not think it is probable that the two forms are specifically identical, as 

 the interiors of the valves of several species of Acrothele appear very much alike. 



Formation and Locality. Middle Cambrian : (C 57) In limestone nodules in 

 the lower shale member of the Kiu-lung group [Blackwelder, 19070, pp. 37 and 40 

 (first list of fossils)], 3 miles (4.8 km.) south of Kao-kia-p'u, and 4 miles (6.4 km.) 

 north of Sin-t'ai-hien, Sin-t'ai district, Shan-tung, China. 



Genus ACROTRETA Kutorga. 



For description and discussion of the genus Acrotreta see Monogr. U. S. 

 Geol. Survey, vol. Li, 1912, pp. 671-674. 



Acrotreta lisani Walcott. 

 Plate 3, Figures 9, qa-c. 



Acrolrela Hani WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxvm, p. 300. (Described and discussed 

 as below as a new species. Li San's name was at that time believed to be correctly written as 

 Lian, hence the form of the specific name.) 



Acrotreta lisani WALCOTT, 1912, Monogr. U. S. Geol. Survey, vol. LI, pp. 692-693, plate LXVIII, figs. 

 3, 3<z-c. (A copy of the preceding reference.) 



Shell small, about 1.5 mm. in diameter; outline of aperture subcircular, the pos- 

 terior 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 of the diameter at its aperture. Dorsal valve slightly convex, apex mar- 

 ginal. Surface of shell marked by fine, concentric striae and lines of growth that on 

 the dorsal valve tend to form low ridges toward the outer margins. 



This species is the representative of the American Acrotreta idahoensis sidcata 

 Walcott [191 2b, p. 690, plate LXV, fig. 5]. It has the same type of false area, and the 

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

 Li San, Mr. Willis's faithful Chinese interpreter. 



Formation and Locality. Middle Cambrian: (C22) Ch'ang-hia limestone in 

 upper oolitic portion [Blackwelder, 190712, pp. 22 and 33 (part of last list of fossils)], 

 at Ch'ang-hia, Shan-tung, China. 



Collected by Eliot Blackwelder. 



Acrotreta pacifica Walcott. 

 Plate 4, Figures i, la-f. 



Acrotreta pacifica WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xxvm, p. 301. (Described as below as 



a new species.) 

 Acrotreta pacifica WALCOTT, 1912, Monogr. U. S. Geol. Survey, vol. n, p. 699, plate LXIX, figs. 6, 6a-e. 



(A copy of the preceding reference.) 



Ventral valve a high cone, with the apex a little in advance of the posterior 

 margin ; base circular, with the exception of a slight flattening on the posterior side ; 

 apex acute and pointing upward ; false area only a slight flattening of the shell from 

 the apex to the margin. The largest ventral valve has a diameter and height of 

 about 1.5 mm. Surface marked by fine, concentric stria? that continue without 

 noticeable deflection across the false area. 



'Mobergiti granulata Redlich, 1901, Mem. Geol. Surv. India, n. ser., vol. I, p. 5, plate I, figs. 11-18. 



