. Cambrian Brachiopoda. Brachiopoda, Fossil. 390 CAJVIBRIAN BRACHIOPODA. Obolus dolatus (Sardeson). Text figures 35A-C. Lingula dolala Sardeson, 1896, Bull. Minnesota Acad. Nat. Sci., vol. 4, p. 95, PI. VI, fig. 12. (Described as a new species.) Only the exterior of the valves of this species is known. The outline of the valves is much like that of Oholus matinalis (Hall) (PI. VIII), and it does not differ more in this respect from. Figure 35.—Obolus dolatus (Sardeson). A, Exterior of a large, crushed ventral valve, the tj'pe specimen. B, Exterior of an elongate dorsal valve. C, Surface ridges
. Cambrian Brachiopoda. Brachiopoda, Fossil. 390 CAJVIBRIAN BRACHIOPODA. Obolus dolatus (Sardeson). Text figures 35A-C. Lingula dolala Sardeson, 1896, Bull. Minnesota Acad. Nat. Sci., vol. 4, p. 95, PI. VI, fig. 12. (Described as a new species.) Only the exterior of the valves of this species is known. The outline of the valves is much like that of Oholus matinalis (Hall) (PI. VIII), and it does not differ more in this respect from. Figure 35.—Obolus dolatus (Sardeson). A, Exterior of a large, crushed ventral valve, the tj'pe specimen. B, Exterior of an elongate dorsal valve. C, Surface ridges on the front part of another dorsal valve, Xl-1. The specimens represented are all from Locality 339, near Stillwater, Miimesota, in beds which are reported by Sardeson to be the Lower Ordovician Oneota dolomite. that species than specimens of 0. matinalis differ from each other. The chief specific distinc- tion is in the fine, narrow, sharp, slightly undulating, slightly inosculating concentric ridges; the spaces between the ridges are about twice the width of the ridges. This surface is some- what similar to that on the interspaces between the beaded ridge of Oholus (Mickvntzella) siluricus (PL XV, fig. Ic). It may be that when specimens of the interior of the valves are found other differences from 0. matinalis will be noted. Oholus dolatus appears to be a Lower Ordovician representative of the widely distributed 0. matinalis. Formation and locality.—Lower Ordovician: (339 [Sardeson, 1896, pp. 95 and 96]) from beds referred by Sardeson to the Oneota dolomite, Stillwater, Washington County, Minnesota. Obolxjs eichwaldi Mickwitz. Obolus eichwaldi Mickwitz, 1896, Mem. Acad. imp. sci. , 8th ser., vol. 4, No. 2, pp. 154-155, PI. 11, figs. 15a-d. (Described and discussed in German as a new species.) Of this species Mickwitz had only the posterior portion of a dorsal valve and some small fragments. He states that the essential characteristics which distinguish i
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