OBOLID^. 533 



Ohservations. — This very pretty little species occurs in abundance in the compact gray 

 limestone of the Black Hills associated with numerous fragments of trilobites and Dicellomus 

 nanus (Meek and Hayden). The more elongate forms strongly resemble Lingulella peratten- 

 uata (Whitfield), which occurs in the Middle Cambrian sandstones on the southern margin 

 of the Black Hills. The species differs, however, from the latter in being more ovate and 

 in having the dorsal valve more obtusely rounded posteriorly. This species may be also com- 

 pared with L. desiderata (Walcott) and L. manticula (White). When flattened in the shales 

 it is difficult to distinguish it from L. desiderata. 



A small shell occurs in the "St. Croix sandstone" of the upper Mississippi region that 

 appears to be identical with this species, Both in its typical form and in its comparatively 

 wide range of variation. With the somewhat abundant supply of material from both the 

 Black Hills and Wisconsin, I am imable to determine any specific differences that are con- 

 stant. The same is true of the form in the limestones south-southwest of Potosi, Missouri, 

 where it is associated with Linnarssonella girtyi Walcott. 



The same range of variation occurs in shells frora the limestone in the upper part of the 

 Keagan sandstone of Oklahoma, and apparently they are identical. 



In the shaly sandstones of the Rome formation in Tennessee casts of an apparently iden- 

 tical form occur (PI. XXI, figs. 3, 3a-d). The variation between the Tennessee and South 

 Dakota shells does not appear to be greater than the range of variation among the shells from 

 the same locality in the Black Hills and the localities where it has been identified in Wisconsin 

 and Minnesota. 



In a limestone at the north end of the Quinn Canyon Range, Nevada, J. E. Spurr, of the 

 United States Geological Survey, collected a number of small shells that appear to be identical 

 with this species. The shells are well preserved and have the general form of surface charac- 

 teristic of the species. A single specimen of a larger ventral valve has all the characteristics 

 of L. Tnanticula (White). 



A shell from Middle Cambrian limestones at Mount Nebo, Wasatch Range, Utah, is doubt- 

 fully referred to this species. It is associated with Micromitra (Iphidella) pannula (White) 

 and Acrotreta nehoensis Walcott. 



Tliis form owes its specific name to its marked resemblance to several other forms, from 

 each of which, however, it is distinct. 



Formation and locality. — Tipper Cambrian: (12m) Arbuckle limestone (in the section 7 miles (11.2 km.) north, 

 of Springer this horizon is about 30 feet (9.1 m.) above the Reagan sandstone), in NE. ^ sec. 2, T. 2 S., R. 1 E., Ard- 

 more quadrangle (U. S. Geol. Survey), Carter County, Oklahoma. 



(12n) Limestone of the Reagan sandstone (in the section 7 miles (11.27 km.) north of Springer this horizon is 

 about 240 feet (73 m.) above the porphyry contact and 40 feet (12 m.) below the Arbuckle limestone), NW. {■ sec. 1, 

 T. 2 S., R. 1 E., Ardmore quadrangle (U. S. Geol. Survey), Carter County; (12k) limestone of the Reagan sand- 

 stone (in the section 7 miles (11.2 km.) north of Springer this horizon is about 225 feet (69 m.) above the porphjay 

 contact and 55 feet (17 m.) below the Arbuckle limestone), on the west side of Honey Creek, near the southeast corner 

 of sec. 35, T. 1 S., R. 1 E., Ardmore quadrangle (U. S. Geol. Sm-vey), Carter County; (12p) about 225 feet (69 m.) 

 above the igneous rocks in the limestone of the Reagan sandstone, at the northwest extremity of the Arbuckle Moun- 

 tains, about 4 miles (6.4 km.) east of Homer, Carter County; all in Oklahoma. 



(9r) About 45 feet (14 m.) above the porphjTy contact in the limestone of the Reagan sandstone, SE. J NE. J 

 sec. 2, T. 4 N., R. 13 W.; (9s) about 85 feet (26 m.) below the Arbuckle limestone in the limestone of the Reagan sand- 

 stone, middle of west half of sec. 13, T. 4 N., R. 13 W.; (9t) about 170 feet (52 m.) above the porphyry contact in the 

 limestone of the Reagan sandstone, SE. } NE. } sec. 2, T. 4 N., R. 13 W.; and (9u) about 195 feet (59.4 m.) above 

 the porphyry contact in the limestone of the Reagan sandstone, 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. 



(328a) "St. Croix sandstone" 4 miles (6.4 km.) north of Winfleld; and (97a and 97c) "St. Croix sandstone" 

 near Winfield; both in Jefferson County, Wisconsin. 



(78b) "St. Croix sandstone" 50 feet (15.2 m.) above St. Croix River, near the landing at Osceola, Polk County; 

 (328n) "St. Croix sandstone" 2 miles (3.2 km.) south of Osceola, Polk County; and (80a) "St. Croix sandstone" 

 4 miles (6.4 km.) north of Reedsburg, Sauk County; all in Wisconsin. 



(86a) "St. Croix sandstone" near Redwing, Goodhue County; (339d) "St. Croix sandstone" at Taylors Falls, 

 Chisago County; (82c) conglomerate beds in the "St. Croix sandstone" in point below Franconia, Chisago County; 



