422 CAMBEIAN BRACHIOPODA. 



depression in the dorsal valve, and also in being flattened across the center of the ventral valve. 

 It occurs at a higher horizon than Oholus (Westonia) chuarensis (Walcott), 0. {W.) euglyphus 

 (Walcott), and Lingulella lineolata (Walcott) of the upper beds of the "Tonto" sandstone. It 

 has more the form of the true Oholus than those species, but its shell is relatively thin and 

 marked by fine radiating strise. All of its essential characters are well shown by the figures 

 illustrating the species. 



Formation and locality. — Tipper Cambrian: (75) Thin-bedded limestones just below the base of the Ordovician 

 in the Tonto group, near the water's edge at the mouth of Kanab Canyon, Grand Canyon of the Colorado, Arizona. 



Middle Cambrian : (74) Sandstone about 300 feet {91.4 m,.) above the base of the Tonto group, at the head of Nunhoweap 

 Valley, Orand Canyon of the Colorado, Arizona. 



(358b) Limestone on the southwest side of Escabrosa Ridge, 4.5 miles (7.2 km.) west-southwest of Bisbee, Arizona. 



Obolus ? zoppi Walcott. 

 Plate XXX, figures 16, 16a-b. 



Obolella crassa Bornemann [not Hall], 1891, Nova Acta Acad. Caes. Leop. -Carol. Germanicae Naturae Curiosorum, 



Bd. 56, No. 3, pp. 439-440, PI. XIX, figs. 15-17. (Described and discussed in German; see below for translation. 



Figs. 16, 17a, and 17b are copied in this monograph, PI. XXX, figs. 16a, 16, and 16b, respectively, 16b being 



the side view of the specimen represented by fig. 16.) 

 Obolus f zoppi Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, pp. 684-685. (Original description translated and species 



discussed as below as a new species.) 



The original description by Bornemann follows : 



Broadly oval or circular, with somewhat pointed vertex. Shells strongly arched, one somewhat more so than the 

 other. They are marked with prominent concentric lines; no radial striation is noticed. Found in a red-yellow 

 sandstone layer not far from the houses of Canal Grande on the road to Punta Pintau, Sardinia. 



In view of the imperfect state of preservation, a determination can only be based on the outer form, whose habit 

 agrees with the American species from the Cambrian limestone of Troy. 



Bornemann kindly sent me two specimens of this form. They suggest Oholella crassa (Hall) 

 in form and outline, but the material is too imperfect to identify the species or genus. I find 

 in one specimen indications of the presence of a high area that rises slightly above the plane 

 of the ventral valve. In two casts there is nothing to suggest the cast of the pedicle aperture, 

 which is usually well preserved in casts of the ventral valve of specimens of Obolella atlantica 

 Walcott. As the material is probably from the Middle Cambrian, a provisional reference is made 

 to Oholus. 



Formation and locality. — Middle Cambrian: (354f [Bornemann, 1891, p. 439])" Reddish-yellow sandstone near 

 the houses of Canal Grande on the road to Punta Pintau, island of Sardinia, Italy. 



Obolus sp. undt. a. 



f 



Plate X, figure 4. 



A small Oholus-like shell, which occurs in the dark argillaceous shales above the Upper 

 Cambrian zone of eastern New York, resembles in outline Oholus (Broggeria) salteri (HoU) 

 (PI. XIII) of England and Sweden. All the specimens are flattened in the shale. No distinc- 

 tive specific characters except a series of well-defined concentric striae are shown. 



Formation and locality. — Ordovician: (338v) Shale 1 mile (1.6 km.) southwest of Middle Granville, Mettawee 

 quadrangle (U. S. Geol. Survey), Washington County, New York. 



Obolus sp. undt. b. 



A small shell marked by very distinct concentric striae and very faint radiating striae occurs 

 at the following locality. The material is too imperfect for illustration. 



Formation and locality. — Upper ? Cambrian: (7n) Limestone at Hornet Spring in the Spring Mountain Range, 

 on road from Indian Spring to Pahrump Valley, Lincoln County, Nevada. 



a Specimens from this locality are included in the collections o( the United States National Musemn . 



