DESCRIPTION OF GENERA AND SPECIES. 79 
“The interior of the brachial valve, as far as known, shows no other characters 
wen the radiating lines, which appear to belong to the ornamentation of the outer 
surface. 
“Shell substance tenuous, apparently corneous. External surface covered with 
more or less prominent, sometimes lamellose concentric growth lines, crossed by fine, 
gently curved, radiating striez which are usually more prominent when the concentric 
lines are exfoliated.” 
Discinopsis sulcatus (Walcott). 
Plate 4, Figure 3. 
Craniella ?? sp. WALCoTT, 1905, Proc. U. S. Nat. Mus., vol. xxrx, pp. 4 and 6. (Listed.) 
Discinopsis sulcatus (WaLcorTr), 1906, idem, vol. xxx, pp. 568-569. (Described and discussed as below 
as a new species.) 
Discinopsis ? sulcatus (WaLcorr), 1912, Monogr. U.S. Geol. Survey, vol. 11, p. 721, plate Lxxx11, fig. 6. 
(Copy of the preceding reference.) 
This species is based upon the cast of the interior of a small ventral valve, that 
in its interior markings closely approaches the interior of the ventral valve of Dis- 
cinopsis gulielmi (Matthew) [Walcott, 1912b, plate LXxxtl, figs. 5, 5a—c]. 
The interior cast shows that the ventral valve was subcircular in outline, 
moderately convex, and with the apex probably perforated by a small, circular 
foraminal aperture. In front of the cast of the base of the foraminal aperture 
there is a broad depression that extends to the front margin; on each side of the 
central depression an elongate, slightly depressed area extends forward and outward 
from near the base of the cast of the foraminal aperture, along the ridge on each 
side of the median depression; back of the base of the foraminal aperture there is 
a narrow, short, arched furrow that indicates the presence of a corresponding ridge 
on the interior of the shell. No other markings are shown on the cast, except the 
faint outline of what may have been the visceral area, on the median line in front of 
the base of the foraminal aperture and between the broad vascular sinuses. 
This species is referred to the genus Discinopsis as the result of comparison 
with specimens of the interior of a ventral valve of D. gulielmi. One interior of 
the latter species has scars much like those shown in D. sulcatus, figure 7. 
Formation and Locality.—Upper Cambrian: (C56) Lower part of Ch’au-mi-tién 
limestone, 25 feet (7.5 m.) below the top of Pagoda Hill [Blackwelder, 19074, p. 42 
(part of last list of fossils)], 1 mile (1.6 km.) west of Tsi-nan, Shan-tung, China. 
Collected by Eliot Blackwelder. 
Genus BILLINGSELLA Hall and Clarke. 
For discussion of the genus Billingsella see Monogr. U. S. Geol. Survey, vol. 
LI, 1912, pp. 749-750. 
Billingsella pumpellyi Walcott. 
Plate 4, Figures 4, 4a—c. 
Billingsella pumpellyi WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvutl, p.242. (Described and 
discussed as below as a new species.) 
Billingsella pumpellyi Wacort, 1912, Monogr. U.S. Geol. Survey, vol. L1, pp. 760-761, plate xcvIl, 
figs. 8, 8a—c. (Copy of the preceding reference.) 
General outline subsemicircular, greatest width at the hinge-line, or a little in 
advance of it; considerable variation exists in the relative proportions of length and 
width; a ventral valve 8 mm. long has a width of 9 mm.; the dorsal valve is more 
transverse, length 5.5 mm., width 8 mm. ‘The ventral valve is strongly convex, 
