PATERINIDiE. 341 



MiCEOMiTEA scuLPTiLis (Meek). 

 Plate III, figures 5, 5a-e. 



Ij^idea (??) sculptilis Meek, 1873, Sixth Ann. Rept. U. S. Geol. and Geog. Survey Terr, for 1872, p. 479. (Described 



and discussed as a new species, and the generic name " Micromitra" proposed in case the species should prove 



to belong to a new genus.) 

 Kutorgina minutissima Hall and Whitfield, 1877, TJ. S. Geol. Expl. 40th Par., vol. 4, pt. 2, pp. 207-208, PI. I, figs. 



11 and 12. (Described and discussed as a new species. The specimens represented by figs. 11 and 12 are redrawn 



in this monograph, PI. Ill, figs. 5b and 5c, respectively.) 

 Kutorgina sculptilis (Meek), Walcott, 1884, Mon. U. S. Geol. Survey, vol. 8, p. 20, PL I, figs. 7, 7a-b, PI. IX, fig. 7. 



(The three specimens represented in PL I, figs. 7 and 7a, PL I, fig. 7b, and PL IX, fig. 7, are redrawn in this 



monograph, PL III, figs. 5, 5b, and 5c, respectively.) 

 Iphidea sculptilis Meek, Schuchekt, 1897, Bull. U. S. Geol. Survey No. 87, p. 235. (Merely goes back to original 



generic reference.) 

 Iphidea sculptilis Meek, Walcott, 1899, Mon. TJ. S. Geol. Survey, vol. 32, pt. 2, pp. 447-448, PL LX, figs. 5, 5a-c. 



(Discussed. The specimen represented by figs. 5, 5a-c is redrawn in this monograph, PL III, fig. 5a.) 

 Iphidella sculptilis (Meek), Walcott, 1905, Proc. TJ. S. Nat. Mus., vol. 28, p. 308. (Merely changes generic reference.) 



In the description of IpTiidea (??) sculptilis, Meek [1S73, p. 479] decided that as the shell 

 had a very narrow, slightly flattened margin on each side, representing a false area, and that 

 as there seemed to be a wide-open triangular foramen, it could be referred to the genus Acro- 

 treta or the genus Iphidea. He was not positive that there was not a permanent pseudodel- 

 tidium present, but assuming the absence of that structure, and tliinking it probable that when all 

 the characters of the shell were knowii it would be found to belong to a different genus, either of 

 the Brachiopoda or of some other group, he proposed for the genus the name " Micromitra." 



A study of the specimens of M. sculptilis collected from the same horizon, at a point not far 

 distant from the original locality, shows the presence of a false area and a pseudodeltidium of 

 the same type as that of Micromitra (JPaterina) hella (Billings). There is, however, a difference 

 in the two forms that is considered of subgeneric value. The surface of M. (P.) iella is covered 

 with fine concentric striae and the surface of Micromitra sculptilis is marked by very fine, sharp, 

 elevated concentric Unes that coalesce or bifurcate irregularly, imparting a peculiarly inter- 

 rupted wavy appearance that is higlily characteristic. The variation in the surface character is 

 continued still further in Micromitra {IpMdella) pannula (White), in which the surface is divided 

 into minute porelike pits by a very fine network of oblique raised fines. Under the lens the 

 surface resembles that of finely woven cloth. 



The most nearly related species is Micromitra Jiaydeni Walcott, which has a similar surface, 

 but the latter has a large pseudodeltidium on the ventral valve, and that valve is more depressed 

 than in M. sculptilis. 



A fragmentary ventral valve from 2,500 feet (762 m.) up in the iEddle Cambrian series of 

 the northern Wasatch Alountains appears to be a form somewhat intermediate between Micro- 

 mitra (Paterina) crenistria (Walcott) and M. sculptilis. It has the surface of the latter except 

 that the radiating ribs are very faint. It occurs in the Blacksmith Fork section, east of Hyrum, 

 Utah. 



Formation and locality. — Upper Cambrian: (61) Limestone in the Dunderberg shale [Walcott, 1908f, p. 184], 

 a little south of the Hamburg mine; and (62) limestone in the Dunderberg shale fW'alcott, 1908, p. 184], in a canyon 

 immediately north of Adams Hill; both in the Eureka district [Hague, 1892, Atlas], Eureka County, Nevada. 



Middle Cambrian: (302) Limestone east of Gallatin River, above Gallatin; and (302a and 302c) limestones at several 

 places on the south side of the Gallatin Valley; both in Gallatin County, Montana. 



(302b) Limestones near Crowfoot Ridge, Gallatin quadrangle (U. S. Geol. Survey), Yellowstone National Park, 

 Wyoming. 



(55n) About 1,850 feet (564 m.) above the Brigham quartzite and 2,350 feet (716 m.) below the Upper Cambrian 

 in the limestones forming 2g of the Bloomington formation [Walcott, 1908f, p. 195], in Blacksmith Fork Canyon, about 

 10 miles (16.1 km.) east of Hyrum, Cache County, Utah. 



(81) Shales believed to be referable to the lower portion of the Marjum limestone [Walcott, 1908f, p. 180], 

 found about 0.5 mile (0.8 km.) east of Antelope Springs; (3x) about 2,200 feet (670.6 m.) above the Lower Cambrian 

 and 2,200 feet (670.6 m.) below the Upper Cambrian in the limestones forming Id of the Marjum limestone [Walcott, 

 1908f, p. 180], 2.5 miles (4 km.) east of Antelope Springs in ridge east of Wheeler Amphitheater; and (lOy) about 2,900 



