PATEKINID^. 339 



/ MiCROMITKA PEALEI (Walcott). 

 Plate III, figures 3, 3a-e. 



Iphidea pealei Walcott, 1897, Proc. U. S. Nat. Mus., vol. 19, pp. 712-713, PI. LIX, figs, a, 3a-c. (Described and dis- 

 cussed as below as a new species. The two specimens represented by figs. 3, 3a-b, and 3c are redrawn in this 

 monograph, PI. Ill, figs. 3, 3a-b, and 3c, respectively.) 



Ventral valve subconical, beak slightly incurving over the pseudodeltidium. Cardinal 

 slope flattened to form a narrow false area, wliicli is clearly defined from the curvature of the 

 shell by a slightly elevated threadlike ridge. Pseudodeltidium comparatively narrow, strongly 

 convex, and arched below. The striae of growth cross the false area and arch over the delthyrium. 



Dorsal valve moderately convex, and without any special characteristics to distinguish it 

 from the same valve in Micromitra {Paterina) bella (Billings), M. (P.) superba (Walcott), and 

 M. (P.) lahradorica (Billings). 



Surface marked by fine concentric strise and lines of growth that are usually plam, but 

 in some examples are slightly crenulated. In such instances fuie radiating lines or stria are 

 also shown. Shell substance corneous. 



In the most perfectly preserved specimens there is a sUght furrow or depression near the 

 ajiex of the ventral valve, but there is no trace of a perforation or apical opening. 



This species approaches M. sculptilis (Meek) in some examples of the ventral valve. It 

 differs mainly in the narrow pseudodeltidium and the character of the surface markings. It 

 might be considered as a form intermediate between M. (P.) iella (BiUings) and M. sculptilis 

 (Meek). 



The specific name was given in honor of Dr. A. C. Peale, of the Hayden Survey, who col- 

 lected the type specimen. 



Formation and locality. — Middle Cambrian: (4n) Limestone about 325 feet (99.1 m.) above the unconformable 

 base of the Cambrian in divide at the head of Jackson Creek (locally known as Sheep Creek), a creek flowing into 

 Jackson Lake about 0.5 mile (0.8 km.) south of its northwestern corner, Teton Mountains, Grand Teton quadrangle 

 (U. S. Geol. Survey), LTinta County, Wyoming. 



(159) Limestones north of West Gallatin (Gallatin) River, Gallatin County; (302) limestone east of Gallatin River, 

 above Gallatin, Gallatin County; (ip) about 225 feet (68.6 m.) above base of Cambrian in limestones interbedded in 

 Flathead shales of Peale [1893, p. 21], on the north side of West Gallatin (Gallatin) River, 2 miles (3.2 km.) north- 

 east of Logan, Threeforks quadrangle (U. S. Geol. Survey), Gallatin County; (155a) limestone north of East Gallatin 

 River, near Hillsdale, Threeforks quadrangle ( TJ. S. Geol. Survey), Gallatin County; (Ha) about 375 feet (114.3 m.) 

 above base of Cambrian in limestone interbedded in the Flathead shales of Peale [1893, p. 21], 1 mile (1.6 km.) north 

 of the junctioii of East Gallatin and West Gallatin (Gallatin) rivers, 4 miles (6.4 km.) east-northeast of Logan, 

 Threeforks quadrangle (U. S. Geol. Survey), Gallatin County; (5f and 340) limestone interbedded in the Wolsey shale 

 [Weed, 1900, p. 285], in Meagher County on road to Wolsey, south of the divide at the head of Sawmill Creek, and 

 about 12 miles (19.3 km.) south of Neihart, Little Belt Mountains quadrangle (U. S. Geol. Survey), Cascade County; 

 (4x) limestone interbedded in the Wolsey shale [Weed, 1900, p. 285], at the base of a butte in Belt Park, about 6 

 miles (9.6 km.) northwest of Neihart, Little Belt Mountains quadrangle (U. S. Geol. Survey), Cascade County; and 

 (91i) limestone on Beaver Creek, 5 miles (S km.) north of York, about 8 miles (12.8 km.) north of Canon Ferry, Big 

 Belt Mountains, Fort Logan quadrangle (U. S. Geol. Siu'vey), Meagher County; all in Montana. 



(74) Sandstone about 300 feet (91.4 m.) above the base of the Tonto group, at the head of Nunkoweap Valley, 

 Grand Canyon of the Colorado, Arizona. 



MiCKOMiTRA PUSiLLA (Lumarsson). 



''' Plate III, figures 2, 2a-c. 



Kutorgina cingulata pusilla Linnars.son, 1876, Bihang till K. svensk. Vet.-Akad. Handl., Bd. 3, No. 12, p. 25, PI. IV, 

 figs. .53 and 54. (Described as below, and discussed in English, as a new variety.) 



Kutorgina cingulata Walcott (in part) [not Billings], 1886, Bull. U. S. Geol. Survey No. 30, pp. 102-104. (Speci- 

 mens now referred to Micromitra pusilla were included with the specimens representing Kutorgina cingulata 

 when this description was written.) 



Kutorgina cingulata pusilla Linnarsson, Matlby, 1902, Quart. Jour. Geol. Soc. London, vol. 58, pt. 1, pp. 146-147, 

 figs. 19 and 20, p. 147. (Discussed from a new locality.) 



Kutorgina cingulata pusilla Linnarsson, Gronwall, 1902, Danmarks Geol. Unders0gelse, Rsekke 2, No. 13, pp. 40-41. 

 (Discussed in Norwegian.) 



