DESCRIPTION OF GENERA AND SPECIES. 87 
Scenella ? dilatatus Walcott. 
Plate 5, Figures 2, 2a. 
Scenella ? dilatatus WALcoTYT, 1906, Proc. U.S. Nat. Mus., vol.xxx, p.570. (Described and discussed 
as a new species essentially as below.) 
This species is based upon two specimens which preserve the expanded outer 
margin, but not the elevated, central, conical portion of the shell. The exterior 
outline is oval, the length of the type specimen being 9 mm.; width, 7mm. The 
surface on the inner side of the campanulate margin is marked by numerous radi- 
ating, elevated striz. As viewed from the lower side the margin slopes gently 
inward to a shallow depression, or furrow, within which there is a rounded, slightly 
elevated ridge, that extends around the border of the elevated portion of the shell, 
except on what is supposed to be the posterior side; on this side the curvature from 
the margin across the border to the elevated portion of the shell is uninterrupted. 
A second specimen occurs in the collection which shows the exterior surface. 
This is smooth, and corresponds in surface configuration approximately to the 
reverse of the specimen above described. Unfortunately it is in a very fragmentary 
state, neither the outline of the margin nor the central, elevated portion being 
preserved. 
This species is distinguished by the broad, campanulate-like border; it differs 
from Scenella clotho |p. 86] in its smooth exterior surface and the strong, radiating 
striz on the inner surface, both the outside and inside of the shell of S. clotho being 
marked by concentric striz and lines of growth. 
Formation and Locality.—Middle Cambrian: (C70) Oolitic limestone about 30 
feet (gm.) above the base of the Ki-chéu limestone [Willis and Blackwelder, 1907, p. 
144 (last list of fossils)], 4 miles (6.4 km.) south-southwest of Tung-yii, Shan-si, China. 
Collected by Eliot Blackwelder. 
Scenella sp. undt. Walcott. 
Plate 5, Figure 4. 
Scenella sp. undt. WALCOTT, 1905, Proc. U. S. Nat. Mus., vol. xx1x, p. 12. (Discussed as below.) 
This species is represented by a cast of the interior of a small patelloid shell, 
with an oval aperture measuring 2 by 3 mm., and having a slightly eccentric, 
elevated apex. It does not appear to be identical with Scenella clotho [p. 86] of the 
Ch’ang-hia formation, as the apex is more eccentric and there is no evidence of any 
carina. In outline it is much like Scenella ? conula Walcott [1884b, p. 15, plate 9, 
fig. 6], but it differs in surface characters and the form of its margin. 
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, 1907a, p. 42 
(part of last list of fossils)], 1 mile (1.6 km.) west of Tsi-nan, Shan-tung, China. 
Collected by Eliot Blackwelder and Li San. 
Genus MATHERELLA Walcott. 
Matherella WaLcort, 1912, Smithsonian Misc. Coll., vol. 57, No. 9, p. 263. (Described and discussed 
as a new genus.) 
Univalve shells, sinistrally coiled; spine composed of rounded volutions that 
are more or less elevated; umbilicus open; peristome, as far as known, entire, united 
with the preceding volution on the inner side, and probably not expanded to any 
considerable extent. 
Genotype.—Matherella saratogensis Walcott [1912a, p. 264]. 
The species Straparollina circe Walcott is referred to Matherella with consider- 
able doubt, but as it is a sinistrally coiled shell with an open umbilicus, rounded 
whorls, and apparently with a relatively small aperture and narrow peristome, it 
is placed in the genus. 
