OBOLIDiE. 575 



Yenchuang, Sintai district, Shantung; and (C32) a fine-grained bluish-black limestone bowlder believed to have come 

 from the lower part of the Kisinling limestone [Blackwelder, 1907b, p. 272], collected in river drift 1 mile (1.6 km.) 

 south of Chonpinghien, on Nankiang River, Eouthern Shensi; both in China. 



DicELLOMUs PECTENOiDEs (Whitfield). 

 Text figures 48A-B; Plate LII, figures 6, 6a-c. 



Obolus pectenoides Whitfield, 1875, Rept. Reconnaissance Black Hills of Dakota, by Ludlow, p. 103, unnumbered 



plate, figs. 1-3. (Described and discussed as a new species.) 

 Obolus f pectenoides Whitfield, 1880, IT. S. Geog. and Geol. Survey Rocky Mtn. Region, Rept. Geology and Resources 



Black Hills of Dakota, by Newton and Jenney, pp. 338-339, PL II, figs. 18 and 19. (Described. The specimens 



represented by figs. 18 and 19 are redrawn in this monograph, PL LII, figs. 6 and 6a, respectively.) 

 Obolella pectenoides (Whitfield), Schuchert, 1897, Bull. U. S. Geol. Survey No. 87, p. 275. (Merely changes generic 



reference.) 

 Dicellomus pectenoides (Whitfield), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 673. (Merely changes generic 



reference.) 

 Dicellomus pectenoides (AVhitfield), Walcott, 1905, idem, vol. 28, p. 316. (Characterized.) 



This is the largest shell of the several species of the genus. A ventral valve 9 mm. long has 

 a width of 11 mm. All that is known of the structure of the sliell indicates that it was like D. 

 politus (Hall) (PI. LII) and D. nanus (Meek and Ha.yden) (PI. IjIII). ' This species differs from 

 all other described species by the anterior posi- 

 tion of the central muscle scars of the dorsal 

 valve, its larger size, and the thickening beneath 

 the visceral cavity of the ventral valve. Area of 

 ventral valve short and mucli like that of D. nanus 

 (PI. LIII, fig. Ic). Specimens from Eau Claire, 

 Wisconsin, show a thickening of the shell beneath 

 the visceral cavity of the ventral valve not unlike ^ ,„ „. „ , .^ .„.,-.«,,> . ^ . ,■ 



-' . . _ Figure iS.— Dicellomus pectenoides (V/hit&eld). A, Cast of m- 



that of Elkania desiderata (Billings) (PL IjI, fig. la). terlor of ventral valve from Locality 78a, "St. Croix sand- 



Tlie interior of the dorsal valve is quite dissimilar f°'^' "' ^■''".c'"!"- ^^'^^^i^ (u. s. Nat. mus. cat. no. 



^ 51909). B, Cast of interior of dorsal valve from Locality 100, 



in the two species. "St. Crolx sandstone" at Menomonie, Dunn County, Wis- 



consin (U. S. Nat. Mus. Cat. No. 51910). v, Visceral cavity; 



Formation and locality.— Upper Cambrian : (151a) Lime- vs, main vascular sinuses; h, central muscle scars, 



stone in point overlooking Churn Canyon, on the west side of 



the Bridger Range; and (158) limestone north of East Gallatin River near Hillsdale, Threeforks quadrangle (U. S. 

 Geol. Survey); both in Gallatin County, Montana. 



(78a) "St. Croix sandstone" in the topmost quarry on Mount Washington, near Eau Claire, Eau Claire County; 

 and (100) "St. Croix sandstone" near Menomonie, Dunn County; both in Wisconsin. 



Middle Cambrian: (355b) Sandstone in the Dead wood formation on Castle Creek, on the west side of the Black 

 Hills; and (164) sandstone in the Deadwood formation in the cliffs on the east side of the valley near Deadwood, Black 

 Hills; both in South Dakota. 



(355c [Whitfield, 1875, p. 103]) Sandstone on French Creek, Black Hills, South Dakota. 



Dicellomus politus (Hall). 



Text figures 16A-B, page 314; 49A-B, page 576;" Plate LII, figures 1, la-k, 2, 2a-i, 3, 4, 4a, 5, 5a-b. 



Obolus appolinus? Owen (not Eichwald), 1852, Rept. Geol. Survey Wisconsin, Iowa, and Minneso*"a, Appendix, 



p. 501, PI. I B, figs. 9, 11, 15, and 20. (Occurrence mentioned.) 

 Lingula polita Hall, 1861, Rept. Supt. Geol. Survey Wisconsin, p. 24. (Described and discussed.) 

 Obolella sp. 3 Billings, 1861, Geol. Survey Canada, Paleozoic Fossils, vol. 1, p. 7. (Characterized.) 

 Obolella sp. 3 Billings, 1861, Report on the Geology of Vermont, vol. 2, p. 946. (Copy of preceding reference.) 

 Lingula ? polita Hall, 1862, Rept. Geol. Survey Wisconsin, vol. 1, p. 435, fig. 1, p. 21. (Generic reference discussed.) 

 Obolella polita (Hall), Billings, 1862, Am. Jour. Sci., 2d ser., vol. 33, p. 421. (Note on the dates of publication of the 



references cited above. Hall, 1861, p. 24, and Billings, 1861, p. 7.) 

 Obolella sp. 3 Billings, 1862, Report on the Economic Geology of Vermont, by Hager, p. 218. (Copj^ of Billings, 



1861b, p. 7.) 

 Lingula polita Hall, Whitfield, 1862, Am. Jour. Sci., 2d ser., vol. 34, p. 136. (Note on the date of the first reference to 



Lingula polita.) 

 Obolella? polita Hall, 1863, Sixteenth Ann. Rept. New York State Cab. Nat. Hist., pp. 133-134, PL VI, figs. 17-21. 



(Described and discussed.) 



a Text figures 16A-B and 49A-B are the same. 



