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Cambrian Geology and Paleontology

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Cambrian Geology and Paleontology SMITHSONIAN MISCELLANEOUS COLLECTIONS PART OF VOLUME LIII CAMBRIAN GEOLOGY AND PALEONTOLOGY No. 3.—CAMBRIAN BRACHIOPODA: DESCRIPTIONS OF NEW GENERA AND SPECIES With Four Plates BY CHARLES D. WALCOTT MWi No. I8I0 CITY OF WASHINGTON PUBLISHED BY THE SMITHSONIAN INSTITUTION October I, 1908 : CAMBRIAN GEOLOGY AND PALEONTOLOGY No. 3.—CA^IBRIAN BRACHIOPODA: DESCRIPTIONS OF NEW GENERA AND SPECIES By CHARLES D. WALCOTT (With Four Plates) This is the eighth paper resuhing from the prehminary studies for Monograph 51 of the U. S. Geological Survey. I expect to use many new generic and specific names in lists of fossils occurring in geo- logic sections and in a forthcoming paper on the classification of the Brachiopoda, and think it is best to describe the fossils before using their names elsewhere. The paper on the classification will be the last of the preliminary papers, as the monograph is now in the editor's hands and should appear in 1909. The previous papers in this series are I. Note on the genus Lingulcpis. American Jour. Sci., 4th ser., Ill, 1897, pp. 404-405. II. Cambrian Brachiopoda : Genera Iphidia and Yorkia, with descriptions of new species of each, and of the genus AcrotJiclc. Proc. U. S. Na- tional Museum, XIX, 1897, pp. 707-718. III. Note on the brachiopod fauna of the quartzitic pebbles of the Car- boniferous conglomerates of the Narragansett Basin, Rhode Island. American Jour. Sci.. 4th ser., VI, 1898, pp. 327-328. IV. Cambrian Brachiopoda : Obolus and Lingtdella, with descriptions of new species. Proc. U. S. National Museum, XXI, 1898, pp. 385-420. V. Cambrian Brachiopoda: Obolella, subgenus Glyptias; Bicia; Obolus, subgenus IVcsfoiiia; with descriptions of new species. Proc. U. S. National Museum, XXIII, 1901, pp. 669-695. VI. Cambrian Brachiopoda: Acrotrcta ; Linnarsson-cUa ; Obolus; with de- scriptions of new species. Proc, U. S. National Museum, XXV, 1902, PP- 577-612. VII. Cambrian Brachiopoda, with descriptions of new genera and species. Proc. U. S. National Museum, XXVIII, 1905, pp. 227-2,^7. There are also a number of Cambrian brachiopoda described in two papers on the Cambrian faunas of China : Caml)rian Faunas of China. Proc. U. S. National Museum, XXIX, 1905, pp. 1-106. Cambrian Faunas of Cliina. Proc. U. S. National Museum, XXX, 1906, PP- 563-595- 53 54 SMITHSONIAN MISCELIvANEOUS COLLECTIONS VOL. 53 Genus MICKWITZIA Schmidt [1888, p. 24] MICKWITZIA OCCIDENS, new. species Plate 7, Figure i There are only crushed and broken specimens of this shell. One of these shows that the apex of the ventral valve was a little above the posterior margin of the shell, very much as in Mickwitzia pre- tiosa. The outline of the valves appears to have been ovate to sub- circular, with the ventral valve moderately convex. The shell is phosphatic or chitinous and built up of three principal layers. The outer layer is thin and thickly set with minute pustules or granules that give the surface a roughened appearance. When the outer layer is exfoliated, which is usually the case, the middle layer presents a smooth, shining surface that is marked by a few concentric striae and numerous fine radiating striae, between which many very minute punctae occur. The inner layer shows minute, irregular, serpentine, rounded ridges, perforated by vertical canals or punctae. An inte- rior of a ventral valve shows the lines of adyance of the antero- lateral muscle scars. The largest shell indicated on the surface of the siliceous shale has a length and width of 12 mm. This species and the generic reference is based on the character of the apex of the ventral valve and the structure and character of the shell. Formation and Locality.—Lower Cambrian : ( i ) Near the base of the section, about 5,500 feet (1,676.4 m.) below the top of the Lower Cambrian, in shaly indurated sandstones, one mile (1.61 km.) east of the Saline Valley road, and 2 to 3 miles (3.22 to 4.83 km.) east-northeast of Waucoba Springs, Inyo County, California. (2) Sandstones on small hill in the salt flat one mile {1.61 km.) northeast of Silver Peak Mill, Silver Peak quadrangle ( U. S. G.S.), Esmeralda County, Nevada} MICKWITZIA PRETIOSA, new species Plate 7, Figure 2 This species is founded on a single specimen of a ventral valve. It has a length of 7 mm. ; width, 6.5 mm. Outline subcircular, slightly convex; apex curved over toward the posterior margin and projecting beyond it. False area short and obscure. Surface marked by radiating, raised lines, that at the front margin show six ' Where there is more than one locality, the one from which the type speci- mens come is italicised. CAMBRIAN BRACHIOPODA—WALCOTT 55 in a distance of two millimeters. Fine papillae are thickly scattered over the surface. They have a tendency to follow concentric lines of growth on some portions of the shell, and on others they appear on low, narrow, serpentine ridges, as in Mickwitsia monilifera (Lin- narsson) [1869, p. 344]. A few large pimctse are scattered here and there over the surface. Inner surfaces and layers of shell unknown. This beautiful shell differs in the details of its surface from M. monilifera; it is also less convex and the apex is nearer the posterior margin. Formation and Locality.—Lower Cambrian : Eophyton sand- stone, at Lugnas, Vestergotland, Sweden. Genus MICROMITRA Meek [1873, p. 479] MICROMITRA HAYDENI, new species Plate 7, Figures 3 and 2i<^ Ventral valve subconical, with a minute beak arching slightly over a strong, arched pseudodeltidium, which is about one-half as long as the height of the valve. Cardinal slope rounded ; a slight angle is indicated by a line where the concentric surface strise bend inward toward the pseudodeltidium across the narrow area; a sharp angle is formed where the convex pseudodeltidium rises abruptly from the area. Dorsal valve moderately convex, most elevated at the small umbo just in advance of the marginal, minute beak; area very low and narrow and without trace of pseudodeltidium as far as now known. Surface marked by fine, concentric, slightly undulating, thread- like strise and a varying number of irregular, more or less inter- rupted, narrow, depressed, rounded, radiating- ridges ; these ridges are usually most numerous at the central portions of the valves. The concentric striae extend across the narrow area and arch over the pseudodeltidium, where they are finer and crowded together, so that all the strise between the apex and the front margin are com- pressed in about one-half the distance on the pseudodeltidium. The adult ventral valve is about 4.5 mm. in length by 5 mm. in width and 2.5 mm. in height, with a pseudodeltidium 1.3 mm. in length. A dorsal valve 2 mm. in length has a height of about 0.5 mm. at the umbo. The shell is rather thick for a species of this size and it is built up of several thin layers or lamellae. Observations.—Micromitra hoydeni differs from the nearest re- lated species, M. scnlptilis (Meek) [1873, p. 479], in having a strong, 56 SMITHSONIAN MISCELIvANEOUS COIvLECTlONS VOL. 53 convex pseudodeltidium, less elevation of the ventral valve, and a thicker shell. .1/. haydciii occurs near the base of the Middle Cam- brian and AI. sculptilis about 2,000 feet (609.6 m.) higher in the section of the Cambrian rocks of Utah and southern Idaho. The speciiic name is given in honor of Dr. F. V. Hayden, geologist and explorer, under whose charge the geology of this region was first studied. Formation and Locality.— ]\Iiddle Cambrian : Limestone of the Langston formation, just above the Cambrian quartzitic sandstone beds, north side of Two Alile Canyon, near its mouth, 2 miles (2)-^^ km.) southeast of JMalad, Oneida County, Idaho. MICROMITRA SCULPTILIS ENDLICHI, new variety This form is represented by a single specimen of a ventral valve. The surface is similar to that of Microiiiitra sciilptilis (Aleek) [1873, p. 479], but the valve is more elongate, less elevated, and larger (5 mm. in diameter) than the specimens of the latter from the type locality. Formation and Locality.—Upper Cambrian : Limestone 2 miles (3.22 km.) north of Aurum, Schell Creek Range, White Pine County, Nevada. Subgenus IPHIDELLA Walcott [1905(7, p. 304] MICROMITRA (IPHIDELLA) LOUISE, new species Plate 7, Figures 4 and 4a In form this species is not unlike Microiiiitra pcalcl (Walcott) [1897/7, p. 712] and the more elongate forms of .1/. {IpliidcUa) paii- iiiila inaladciisis (Walcott) [1905a, p. 306]. It diiTers from both species mentioned in its surface characters. In the latter respect it is more like AI. (I.) iiyssa (see p. 57), but the form of AI. (/.) Ionise is more elongate and the apex of the ventral valve is nearer to the posterior margin ; the shell also appears to have been thicker. The surface characters are exceedingly minute. Under a glass magni- fying twenty diameters, the surface looks much like that of AI. (/.) pannula (White) [1874, p. 6]. The largest ventral valve in the collection has a length of 7.5 mm. and a width of 7 mm. ; elevation, I muL Alicroiuitra (Ipfiidclla) loitisc is the oldest brachiopod known from the Cambrian of the Canadian Rocky Mountains. In the Lakes Louise and Agnes section it is 3,100 feet (944.9 m.) below the sum- mit of the Lower Cambrian and 2,750 feet (838.2 m.) below the CAMBRIAN BRACK lOPODA WALCOTT 57 horizon which, on the basis of the associated faunas, is correlated with that at which .1/. (/.) nyssa occurs in Montana. It occurs in a fine, hard, dark gray, siHceous shale in association with Hyolithes, Cntaiaiia, and a fragment indicating the free cheek of a trilobite.
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