BILLINGSELLID^. 791 



side of Honey Creek, near the southeast corner of sec. 35, T. 1 S., R. 1 E., 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 porphyry contact and 40 feet (12 m.) below the Arbuckle limestone), NW. 

 J sec. 1, T. 2 S., R. 1 E., Ardmore quadrangle (TJ. S. Geol. Survey), Carter County; and (12p) about 225 feet {69 m.) 

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

 about 4 miles {6.4 hn.) 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; (68) limestone on Packsaddle Mountain, Llano County; 

 and (71) limestone in Cold Creek Canyon, Burnet County; all in Texas. 



(150a) Limestone on the east side of Dry Creek, above the mouth of Pass Creek; and (153a) limestone in ravine 

 on west side of Dry Creek, near the mouth of Pass Creek; both about 5 miles (8 km.) north of Hillsdale, Threeforks 

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



(151) Limestone in point overlooking Churn Canyon, on the west side of the Bridger Range, Gallatin County, 

 Montana. 



(302e) Limestone near the top of the Deadwood formation, in Middle Popo Agie Canyon, near Lander, Fremont 

 County, Wyoming. 



Middle Cambrian: (369a) Limestone in or just beneath the "Edgewise beds" near Elvins, C miles (9.6 km.) 

 south of Bonneterre, St. Francois County, Missouri. 



EOORTHIS WICHITAENSIS LJSVIUSCULUS (Walcott). 

 Plate XCIV, figures Ip-s. 



Orthis {Plectorthis) wichitaensis Ixviusculus Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 272. (Characterized 

 essentially as below as a new variety.) 



A variety with small, narrow, numerous ribs is given the above name. So many grada- 

 tions exist between it and the typical forms of E. wichitaensis (Walcott) that the figures are 

 arranged on the plate rather to show the gradations in surface characters than to bring out 

 this special variety. 



FoBMATio>f AND LOCALITY. — Tipper Cambrian: (12k) Limestones of the Reagan sandstone (in the section 7 

 miles (11.2 km.) north of Springer this horizon is about 225 feet (69 m.) above the porphyry 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. 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 porphyry 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 (12p) 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 at north end of gorge opposite the north end of Sponge Mountain, 2 miles (3.2 km.) south of 

 the San Saba County line; and (68) limestone in Packsaddle Mountain; both in Llano County, Texas. 



EOORTHIS WIMANI (Walcott). 



Plate XCV, figures 4, 4a-d. 



Orthis {Plectorthis) wimani Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 272. (Discussed essentially as below as a 

 new species.) 



Orthis {Plectorthis) wimani Walcott, Moeero and Segbrberg, 1906, Medd. fran Lunds geol. Faltklubb, Ser. B, No. 2 

 (Aftryck ur K. Fysiografiska Siillskapets Handl., N. F., Bd. 17), p. 70, PI. II, figs. 4, 4a-d; PI. Ill, figs. 14, 

 15a-b. (Discussed in Swedish. Figs. 4, 4a-d, in common with the remaining figures on PI. II of Moberg and 

 Segerberg's paper, were copied from a preliminary photograph of PI. XCV of this monograph.) 



This shell is distinguished from EoorfMs christianise (Kjerulf) and E. daunus (Walcott) by 

 the rounded, narrow, simple ribs and the less transverse and more rounded outline. A ventral 

 valve discovered after the drawings were made shows a well-defined pseudospondylium, with 

 the tripartite division as seen in E. remnicha (Winchell) (PL XCI, fig. Ic). Two strong main 

 vascular sinuses extend forward from the lateral divisions of the umbonal cavity nearly to 

 the front of the valve, corresponding in position to those of the dorsal valve (PL XCV, fig. 

 4a) . The cast of the dorsal valve indicates the presence of rather strong crura, crural plates, 

 dental sockets, and delthyrium. 



The ventral valve is rather strongly convex, and the dorsal valve about half as much so. 

 The average size is 6 to 7 mm. in diameter, the ventral valve being about 1.5 mm. larger 



