OBOLIDiE. 411 



Observations. — This somewhat peculiar species is associated with Obolus namouna Walcott, 

 Dicellomus politus (Hall), and Oholus matinalis (Hall). The dorsal valves are clearly distinct 

 from any described form, approaching in some respects the elongate dorsal valve of Lingulella 

 (Lingulepis) acuminata (Conrad) (Pis. XL to XLII), differing, however, in being narrow and 

 more elongate; the ventral valves appear to be broader in proportion than the dorsal valve 

 and approach 0. matinalis (Hall) (PL VIII) in outline but are more elongate. 



Formation and locality. — Upper Cambrian: (98) "St. Croix sandstone" at Eau Claire, Eau Claire County, 

 Wisconsin. 



Middle Cambrian: (84) "St. Croix sandstone" at Dresbach, opposite the mouth of Black River, Winona County, 

 Minnesota. 



Obolus? rokitzanensis Barrande. 



Plate XII, figure 6. 



Obolus? rohitzanensis Baerande, 1879, Syst6me silurien du centre de la Boheme, vol. 5, PL CXXVI, fig. ii: 5. (No 

 text reference. Fig. 5A is copied in this monograph, PI. XII, fig. 6.) 



Barrande gives only one illustration of this species. It recalls to mind those forms of 

 Obolus which preserve the radial striation on the interior surface. The configuration of the 

 visceral area also suggests that of the ventral valve of Oholus. The illustration is introduced 

 in order that the student may have before him a representation of all of the Obolus-like shells 

 known to me. - Figure 5 of Barrande [1879b, PI. CXXVI] should be compared with the ventral 

 valve of Obolus complexus Barrande (PI. XII, fig. 3, of this monograph), and for the radial 

 striation with Plate XII, figure 3b. 



The specific name is derived from Rokitzan, the type locality. 



Formation and locality. — Lower Ordovician: (303b [Barrande, 1879b, PI. CXXVI]) Etage dl in the environs of 

 Rokitzan, Bohemia, Austria-Hungary. 



Obolus kotundatus (Walcott). 

 Plate XX, figures 2, 2a-e. 



Obolus (Lingulella) rotundatus Walcott, 1898, Proc. U. S. Nat. Mus., vol. 21, p. 415. (Characterized as a new species; 



see first paragraph below for copy.) 

 Obolus (Lingulella) desideratum Walcott, 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, pp. 445-446, PI. LX, fig. 2a 



(not fig. 2, referred to Lingulella desiderata). (Described and discussed. The specimen represented by figure 



2a is redrawn in this monograph, PI. XX, fig. 2e.) 



This small species is associated with Lingulella manticula (White). It differs from it in 

 its nearly circular form and more strongly pitted or punctate interior of the valves. A cast of 

 the interior of a dorsal valve shows a well-defined area, the cast of the median ridge and sep- 

 tum, and the central muscle scars. The ventral valve has a length of 3.5 mm., width 3 mm.; 

 dorsal valve, length 3 mm., width 3 mm. 



The shells represented by Plate XX, figures 2 and 2a, are associated in the same hand 

 specimens of limestone with Lingulella manticula. The specimens represented by Plate XX, 

 figures 2b, 2c, and 2d, are from the Upper Cambrian beds of the Gallatin Valley, IVIontana, 

 but so far as can be determined from the material at hand for comparison they appear to 

 represent the same species. 



Formation and locality. — Lower Ordovician: (313d) Limestone at Schellbourne, Schell Creeh Range, White 

 Pine County, Nevada. 



TTpper Cambrian: (160a) Sandstone west of Bear Creek, south of the Gallatin Valley, southwest of Bozeman, 

 Threeforks quadrangle (U. S. Geol. Survey), Gallatin County, Montana. 



(30q) Limestones about 2,300 feet (701 m.) above the Cambrian quartzites, on pipe line above limekiln, in 

 Ogden Canyon, 1 mile (1.6 km.) above its mouth, east of Ogden, Weber County; (34i) shales about 1 mile (1.6 km.) 

 northeast of Sand Pass, at the south end of the Fish Spring Range, Juab County; (33d) thin-bedded blue limestone 

 at the base of the first high point southwest of the J. J. Thomas ranch, on the east side of the Pish Spring Range, Juab 

 County; (30y) about 1,400 feet (426.7 m.) above the Middle Cambrian and 1,900 feet (579.1 m.) below the top of the 

 Tipper Cambrian in the supposed metamorphosed equivalent of the shales forming lb of the Orr formation [Walcott, 

 1908f, p. 176], above the granite contact on top of the ridge north of Notch Peak [Walcott, 1908f, Pis. XIII and XIV], 

 House Range, Millard County; and (34r) limestones 1.5 miles (2.4 km.) northwest of Wahwah Spring, about halfway 

 up the section to the north of the road at Cane Pass, Wahwah Mountains, Beaver County; all in Utah. 



