DESCRIPTION OF GENERA AND SPECIES. 87 



Scenella ? dilatatus Walcott. 



Plate 5, Figures 2, 20. 



Scenella ? dilatatus WALCOTT, 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, 7 mm. The 

 surface on the inner side of the campanulate margin is marked by numerous radi- 

 ating, elevated striae. 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 

 strise on the inner surface, both the outside and inside of the shell of 5. clotho being 

 marked by concentric strise and lines of growth. 



Formation and Locality. Middle Cambrian: (070) Oolitic limestone about 30 

 feet (gm.) above the base of the Ki-chou 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. xxix, 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 f conula Walcott [18846, p. 15, plate 9, 

 fig. 6], but it differs in surface characters and the form of its margin. 



Formation and Locality. Upper Cambrian: (056) Lower part of Ch'au-mi-tien 

 limestone, 25 feet (7.5 m.) below the top of Pagoda Hill [Blackwelder, 19070, p. 42 

 (part of last list of fossils)], i mile (1.6 km.) west of Tsi-nan, Shan-tung, China. 



Collected by Eliot Blackwelder and Li San. 



Genus MATHERELLA Walcott. 



Matlierella WALCOTT, 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. Matlierella saratogensis Walcott [19120, p. 264]. 



The species Straparollina circe Walcott is referred to ]\Iathcrella 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. 



