BILLINGSELLID^. 781 



the general appearance of convexity and rotundity of the ventral valve. This may be seen 

 by comparing the shells marked W=E. wichitaensis with those marked X = S. indianola in 

 Plate XCIV, figure lu, which represents- a fragment of limestone in which the two species are 

 associated. Wlien the specimens of the two species are imperfect or the young shells of E. 

 wicMtaensis occur in association with the shells of E. ind,ianola it is difficult to determine 

 positively to which species they belong. 



The specific name is derived from Indian Territory (now Oklahoma), in which the type 

 specimen was found. 



Formation and locality. — Upper Cambrian: (369) Sandstones at the base of the Elvins formation, in the eastern 

 limits of the town of Flat River, St. Francois County; and (369b) limestone near Potosi, Washington County; both in 

 Missouri. 



(9t) About 170 feet (52 m.) above the porphjrry contact in the limestones of the Reagan sandstone; and (9u) 

 about 195 feet (59.4 m.) above the porphyry contact in the limestones of the Reagan sandstone; both in the SE. \ 

 NE. i sec. 2, T. 4 N., R. 13 W., about 15 miles (24.2 km.) northwest of Fort Sill, Comanche County, Oklahoma. 



(9w) About 100 feet (30.5 m.) below the Arbuckle limestone, in the limestones of the Reagan sandstone, SW. \ 

 eec. 17, T. 4 N., R. 12 W., about 11 miles (17.6 km.) northwest of Fort Sill, Comanche County, Oklahoma. 



(12k) Limestones of the Reagan sandstone {in the section 7 miles {11.2 hm.) north of Springer this horizon is about 

 225 feet {69 m.) above the ■porphyry contact and 65 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. IE., Ardmore quadrangle { U. S. Geol. Survey), Carter County; 

 (12n) limestones of the Reagan sandstone (in the section 7 miles (11.2 km.) north of Springer this horizon is 

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

 T. 2 S., R. 1 E., Ardmore quadrangle (U. S. Geol. Siu-vey), Carter County; and (13p) about 225- feet (69 m.) above 

 the igneous rocks in the limestones of the Reagan sandstone, at the northwest extremity of the Arbuckle Mountains, 

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



(14b) Limestone on Cold Creek at north end of gorge opposite the north end of Sponge Mountain, 2 miles (3.2 

 km.) south of the San Saba County line, in Llano County; and (71) limestone in Cold Creek Canyon, Burnet County; 

 all in Texas. 



Specimens that are doubtfully referred to this species occur at the following locality: 



Upper Cambrian : (68) Limestone on Packsaddle Mountain, Llano County, Texaa 



EooETHis joHANNENSis (Matthew). 

 Plate XCVII, figures 10, 10a. 



Orthisina{f) johannensis Matthew, 1892, Trans. Roy. Soc. Canada for 1891, 1st ser., vol. 9, sec. 4, No. 5, pp. 49-50, 

 PI. XII, figs. 13a-c. (Described and discussed as a new species; see below for copy. The specimens repre- 

 sented by figs. 13a-c are redrawn in this monograph, PI. XCVII, figs. 10 and 10a, respectively.) 



Orthis {Plectorthis) johannensis (Matthew), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, pp. 265-266. (Original 

 description copied and species discussed as below.) 



The original description by Matthew follows : 



Shell subquadrate, doubly convex, rather flat, very thin. 



Dorsal valve depressed at the sides and front, and having a broad, shallow median sinus. The valve is about 

 one-quarter wider than long, and the hinge line is nearly as long as the length of the shell. Umbo slightly elevated, 

 hinge plate weak and thin. 



Ventral valve depressed at the sides, and having a few median ridges running from the umbo to the front of the 

 shell. This valve is somewhat geniculated at two-fifths of its length from the umbo, and from the bend faintly raised 

 ridges diverge to the anterior angles of the shell ; behind the geniculation the surface of the shell is marked by faint 

 undulations similar to those of Strophomena rhomboidalis. 



The umbo is not prominent, but the back of the valve is regularly curved and the area rather low. 



Closely set striae radiating from the umbo and faint concentric striae mark the shell. 



Length of the ventral valve, 9 mm.; width, 10 mm. Length of dorsal, 8 mm.; width, 10 mm. 



This species has a low umbo for an Orthisina, and in its form recalls the genus Strophomena, as also do the con- 

 centric undulations that are found on the back of the ventral valve. The dorsal valve, however, is convex, and the 

 area of this and the ventral valve too high for a Strophomena. It does not appear to agree with any described species 

 of Orthisina. It resembles 0. orientalis White somewhat in form, but is not so long nor so wide at the hinge. From 

 0. pepina Hall it differs in its lower umbo and area, shorter hinge, and smoother surface. It approaches more closely 

 to the form from the Potsdam sandstone of the West, figured by Hall [1863, PL VI, fig. 22], but not named, except 

 as ' ' Strophomena or Strophodonta. ' ' 



Doctor Matthew very kindly sent me the types of tliis species. There is little that can 

 be added to his very complete description, but I had two enlarged drawings made to illustrate 



