86 RESEARCH IN CHIXA. 



General form irregularly oval, with the ventral view obtusely angular toward 

 the apex; rounded, biconvex, with a deep mesial sinus on the ventral valve and a 

 strong median fold on the anterior half of the dorsal valve. 



Surface smooth, with the exception of a few concentric striae and lines of growth. 



The ventral valve has a strong median sinus that occupies about one-third 

 of the width of the valve at the anterior margin and projects forward to fit into 

 the fold in the front of the margin of the dorsal valve ; the sides of the median sinus 

 are elevated, and, with the downward curving lateral slopes, form a strong rounded 

 ridge on each side of the sinus ; none of the specimens in the collection shows the 

 area, but from the profile of the valve it must have been of moderate height, with 

 a rather sharp apex curving over it. 



Dorsal valve with a minute apex from which a narrow, slightly developed 

 median fold extends out to about the center of the shell, where it becomes elevated 

 and projects forward to the front margin ; the remaining portions of the surface are 

 uniformly convex, sloping away from the median fold to the margins of the valve. 



Nothing is known of the interior of either valve. 



In general form this species resembles Syntrophia primordialis (Whitfield) 

 [Walcott, 1912:), plate en, figs. 2, 2a-c] of the St. Croix sandstone of Wisconsin. It 

 differs in its more rounded, irregularly oval form and the very large median sinus 

 of the ventral valve. 



Formation and Locality. Upper Cambrian : Lower part of Ch'au-mi-tien lime- 

 stone [Blackwelder, 19070, p. 42 (part of last list of fossils)], (C56) 25 feet (7.5 in.) 

 below the top of Pagoda Hill, i mile (1.6 km.) west of Tsi-nan, and (C54) near top of 

 limestone knoll two-thirds of a mile (i.i km.) west of Tsi-nan, Shan-tung; also 

 (Cfi-1), upper limestone member of the Kiu-lung group [Blackwelder, 19070, pp. 37 

 and 42 (first list of fossils), and fig. 10 (bed 20), p. 38], 2.7 miles (4.3 km.) southwest 

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



Collected by Eliot Blackwelder and Li San. 



GASTROPODA. 



Genus SCENELLA Billings. 

 Scenella clotho Walcott. 



Plate 5, Figures 3, 30 . 



Scenella dolho WALCOTT, 1905, Proc. U. S. Nal. Mus., vol. xxtx, p. 12. (Described and discussed 

 as a new species essentially as below, i 



Shell small, moderately convex; apex elongate, slightly eccentric, elevated; 

 aperture irregularly oval; a narrow carina extends from the apex down to the 

 broader end, and several obscure carinae radiate from the apex toward the margin. 



Surface marked by fine concentric striae and very fine radiating striae. 



The type specimen has a length of 4.25 mm. ; greatest width, 3 mm. ; elevation 

 of apex, about 1.5 mm. 



This species is clearly distinguished by the broad, elliptical, or subovate form 

 of its aperture, and elongated apex; the latter feature is determined from the 

 interior of the shell, which indicates that the apex was situated somewhat near 

 the narrower end of the aperture; this feature suggests that if there were perfect 

 specimens representing the species, it might be found to be more nearly related to 

 some forms of Stenotheca than to Scenella. 



Formation and Locality. Middle Cambrian : ( (' 18) Dark gray oolitic limestone 

 about 400 feet (120 m.) above the base of the Ch'ang-hia limestone [Blackwelder, 

 19070, p. 33 (third list of fossils)], in cliffs i mile (1.6 km.) east of Ch'ang-hia, 

 Shan-tung, China. 



Collected by Eliot Blackwelder. 



