578 CAMBRIAN BEACHIOPODA. 



(9x) Sandstones lying between beds of quartzite underlying tbe 300 feet of limestone at the top of the Reagan 

 sandstone, SW. J sec. 17, T. 4 N., R. 12 W., about 11 miles (17.7 km.) northwest of Fort Sill, Comanche County, 

 Oklahoma. 



Upper? Cambrian: (358a) Siliceous limestone on Ash Creek, in Pinal County, Arizona. 



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

 County; (339e) "St. Croix sandstone" on Mountain Island, in Mississippi River, just above the mouth of Trem- 

 pealeau River; and (84s) "St. Croix sandstone" near Dakota, Winona County; all in Minnesota. 



(79x) "St. Croix sandstone" near the flour mill on Beaver Creek, north of Galesville; and (328g) "St. Croix sand- 

 stone," Wisconsin shore of Mississippi River, near Trempealeau; both in Trempealeau County, Wisconsin. 



(167) Sandstone beneath limestone and resting on pre-Cambrian "slates, schists, and pegmatites" in bluff 9 

 miles (14.4 km.) west of Custer, Black Hills; (355e) sandstone in the central part of the Black Hills; and (355) sand- 

 stones in Red Canyon a Creek , southwest side of the Black Hills; all in South Dakota. 



(11m) Drill cores of limestone in the Bonneterre limestone at horizons 10 and 20 feet (3 and 6 m.) above the 

 Lamotte sandstone, at Flat River, St. Francois County, Missouri. 



(329b) Thin-bedded limestone collected by the Wheeler Siu-vey in Utah. 



(5k) Limestone in Meagher County, on the road to Wolsey, about 1 mile (1.6 km.) south of the divide at the 

 head of Sawmill Creek, and 8 miles (12.8 km.) south of Neihart, Little Belt Mountains quadrangle (U. S. Geol. Sur- 

 vey), Cascade County; (302k) limestone near Gallatin, Threeforks quadrangle (U. S. Geol. Survey), Gallatin County; 

 (302s) b dark siliceous shale in a quarry in Last Chance Gulch, south slope of Mount Helena, 1.5 miles (2.4 km.) 

 south of Helena, Lewis and Clark County; and (340f) lowest beds exposed at the mouth of Bear Creek, Little Belt 

 Mountains; all in Montana. 



DiCELLOMUS PROLIFICTJS Walcott. 



Plate LXXXIX, figures 10, lOa-b. 



Dicellomus prolificus Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 77, PI. VIII, figs. 3 and 3a. (Char- 

 acterized and discussed as below as a new species. Figs. 3 and 3a are copied in this monograph, PI. LXXXIX, 

 ■ figs. 10 and 10b, respectively.) 



This species differs from Dicellomus politus (Hall), to which it appears to be most nearly 

 related, by the greater convexity of the ventral valve, its higher umbo, and, in most shells, 

 a greater narrowing toward the apex. The dorsal valve differs from that of D. politus in 

 being more rounded on the cardinal margins. It is also to be noted that no traces of muscle 

 scars or vascular markings have been observed on many interiors and casts of the interior 

 of the valves, wliile in D. politus they are prominent on most casts and often on the interior 

 of the valves. The range of outline of the valves of D. politus might include those of D, pro- 

 lificus, but the convexity of the ventral valve and the smooth interior seem to distinguish the 

 latter species. 



Great numbers of the separated valves occur in several thin layers of gray limestones near 

 the summit of the cliffs on the south side of Marjum Pass. 



Formation and locality. — Middle Cambrian: (lOz) About 2,900 feet (884 m.) above the Lower Cambrian 

 and 1,500 feet (457.2 m.) below the Upper Cambrian in the central part of the limestone forming la of the Marjum 

 limestone [Walcott, 1908f, p. 179], in the long cliff about 2 miles (3.2 km.) southeast of Marjum Pass [Walcott, 1908f, 

 Pis. XIII and XV], House Range, Millard County, Utah. 



Dicellomus sp. undt. Walcott. 



Plate LII, figures 7, 7a. 



Dicellomus sp. undt. Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 319. (Mentioned as below as a possible new 

 species.) 



A single specimen of a ventral valve very much like that of Dicellomus appalacJiia (Wal- 

 cott) occurs with material from the Paradoxides forclihammeri zone at Andrarum. A series of 

 specimens would probably prove that it is the representative of an undescribed species. 



Formation and locality. — Middle Cambrian: (3101) Paradoxides forchhammeri zone at Andrarum, 20 miles 

 (32.2 km.) northwest of Simrishamn, Province of Christianstad, Sweden. 



a Some of the specimens arelabeled asfrom Redwater Canyon and some as from Red Canyon Creek, the former locality being given by Whitfield 

 [1882, p. 340). 



b The specimens from this locality are somewhat doubtfully referred to this species. (See PI. LII, figs. -4 and 4a.) 



