ACROTRETID^. 667 



of the cast of a rather strong median ridge; they are elongate oval in outline, the major axis 

 inclining posteriorly toward the median ridge. Wliat may be the impression of an antero- 

 lateral scar occurs on the median ridge a little in advance of the central scars. 



Ohservations. — Linnarssonella girtyi differs from L. minuta (Hall and Whitfield) in the 

 greater convexity of the ventral valve and the median ridge of the dorsal valve. The Oklahoma 

 specimens show a longer false area (PI. LXXIX, fig. Iq") on some shells but on others it is 

 much like that of L. girtyi from the Black Hills. 



The specific name is given in recognition of the paleontologic work of Dr. George H. Girty. 



Formation and locality. — Upper Cambrian: (369) Sandstone in the Blvins formation in the eastern limits of the 

 town of Flat River, St. Francois County, Missouri. 



(9q) About 10 feet (3 m.) above the porphyry contact and 90 feet (27.4 m.) below the Arbuckle limestone, in 

 limestone of the Reagan sandstone, in middle of W. J sec. 2, T. 4 N., R. 13 W.; (9r) about 45 feet (14 m.) above the 

 porphyry contact in the limestone of the Reagan sandstone, in SE. } NE. J sec. 2, T. 4 N., R. 13 W.; and (9p) about 

 160 feet (48.8 m.) above the porphyry contact in the limestone of the Reagan sandstone, in SE. J NE. J sec. 2, T. 4 

 N., R. 13 W.; all about 15 miles (24.2 km.) northwest of Fort Sill, Comanche County, Oklahoma. 



(9v) Limestone of the Reagan sandstone, about 250 feet (76 m.) below the Arbuckle limestone, SW. J sec. 17, T. 

 4 N., R. 12 W., about 11 miles (17.7 km.) northwest of Fort Sill, Comanche County, Oklahoma. 



(12p) About 225 feet (69 m.) above the igneous rocks in the limestone of the Reagan sandstone at the northwest 

 extremity of the Arbuckle Mountains, about 4 miles (6.4 km.) east of Homer, Carter County, Oklahoma. 



(14i) Limestone 1 mile (1.6 km.) west of Cherokee, San Saba County, Texas. 



(32t) Limestone about 3,650 feet (1,112.5 m.) above the Cambrian quartzitic sandstones, in Fandango Spring 

 canyon on the east side of the Dugway Range, about 5 miles (8 km.) north of where the stage road between Vernon 

 and Deep Creek crosses the divide, Tooele County, Utah. 



Middle Cambrian: (88a) Limestone about 100 feet (30.5 m.) above the quartzitic sandstone at the base of the Cambrian, 

 in the northern suburbs of Deadwood; (165) limestone on the east side of the valley in railroad cut about 1 mile (1.6 

 km.) below the main part of Deadwood; and (17k) limestone thrown out on the dump of the Great Northern shaft, 

 southeast of Twobit; all in the Black HUls, South Dakota. 



(Ilk) Limestones of the "Edgewise beds," beneath the Elvins formation, St. Francois County; and (lie) thin- 

 bedded limestone south-southwest of Potosi, Washington County; both in Missouri. 



(313e) Limestone 2 miles (3.2 km.) west of Green's ranch, White Pine County, Nevada. 



A shell that is somewhat doubtfully referred to this species occurs at the following locality : 



Upper Cambrian: (9q) About 10 feet (3 m.) above the porphyry contact and 90 feet (27.4 m.) below the Arbuckle 

 limestone, in limestone of the Reagan sandstone, in middle of W. | sec. 2, T. 4 N., R. 13 W., about 15 miles (24,2 

 km.) northwest of Fort Sill, Comanche County, Oklahoma. 



Linnarssonella minuta (Hall and Whitfield). 



y 



Plate LXXIX, figures 2, 2a-b. 



lAngulepis? minuta Hall and Whitpield, 1877, U. S. Geol. Expl. 40th Par., vol. 4, pt. 2, pp. 206-207, PI. I, figs. 3 



and 4. (Described and discussed as a new species. The specimens represented by PI. LXXIX, figs. 2, 2a-b, 



occur on the same hand specimen of sandy shale as the specimens figured by Hall and Whitfield, but they are 



not the same specimens.) 

 I/ingulepis? minuta Hall and Whitfield, Walcott (in part), 1884, Mon. U. S. Geol. Survey, vol. 8, p. 13. (Localities 



and range mentioned, see p. 668.) 

 Obolella? minuta (Hall and 'V^Tiitfleld), Walcott, 1897, Am. Jour. Sci., 4th ser., vol. 3, p. 404. (Merely changes 



generic reference.) 

 Lingulella minuta (Hall and Whitfield), Schuchert, 1897, Bull. U. S. Geol. Survey No. 87, p. 257. (Merely changes 



generic reference.) 

 Obolella minuta (Hall and Whitfield), Walcott, 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, p. 443. (Merely changes 



generic reference.) 

 Acrotreta minuta (Hall and Whitfield), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 673. (Merely changes generic 



reference.) 

 Linnarssonella minuta (Hall and Whitfield), Walcott, 1902, idem, vol. 25, pp. 603-604. (Described and discussed 



as below.) 



Shell small; general form broad ovate, with the ventral valve slightly subacuminate. 

 The convexity of the two valves is nearly the same and in each the minute beak appears to 

 be at the posterior margin. The false area of the ventral valve is small and divided midway 

 by a faint, narrow pseudodeltidium; it is on the plane of the margin of the valve. Pedicle 



