350 CAMBRIAN BRACHIOPODA. 



about 1 mile (1.6 km.) above ita mouth, east of Ogden, Weber County; (30u) about 250 feet (76.2 m.) above the top of 

 the Cambrian quartzitic sandstones, in sandy shales, 4 miles (6.4 km.) northwest of Promontory Point (on the 



" Lucin cut-off " of the Union Pacific Railway), about halfway 

 up west end of ridge, north of Great Salt Lake, Boxelder County; 

 (34m) limestone about 765 feet (233.2 m.) above the Brigham 

 quartzite fWalcott, 1908a, p. 8], 1 mile (1.6 km.) northwest of 

 Geneva (Copenhagen), east of Brigham, Boxelder County; and 

 (32d) shales about 150 feet (45.7 m.) above the Brigham quartz- 

 ite [Walcott, 1908a, p. 8], on the east side of the south fork of 

 Paradise Dry Canyon (locally known as East Fork), east of Par- 

 adise, Cache Valley, Cache County; all in Utah. 

 ^' (54a) About 750 feet (228.6 m.) above the Brigham quartzite 



Figure 2i.- Micmmitra {Paterina) labmdorica utahemis (Wal- and 3,440 feet (1,048.5 m.) below the Upper Cambrian in the 

 cott). A, A', A", Top.side, and back views of a ventral valve shales forming 2a of the Ute limestone [Walcott, 1908f, p. 196]; 

 from Locality 64m, Middle Cambrian limestones in Blacksmith (g^o) about 900 feet (274.3 km.) above the Brigham quartzite 

 I-ork Canyon, Cache County. Utah (U. S. Nat. Mus. Cat. No. ^^^ 3 j^^^ g ^^ ^^^^^ ^^^ ^ Cambrian in the 



51434). 



»- limestone beds forming lb of the Ute limestone [Walcott, 1908f, 



p. 196]; and (54m) about 1,225 feet {S73A m.) above the Brigham quartzite and 2,950 feet (899.2 m.) below the Upper Cam- 

 brianin the upper part of the limestone forming la of the Ute limestone [Walcott, 1908f, p. 195]; all in Blacksmith Fork 

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



MicROMiTRA (Paterina) labradorica var. undt. 



This form is distinguished from Micromitra (Paterina) labradorica (Bilhngs) and its varie- 

 ties by having much finer and more closely arranged concentric striae. In other characters it 

 approaches very closely to the typical forms of the species. 



Formation and locality. — Lower Cambrian: (Iv) Shales of No. 3 of the Silver Peak group, Barrel Spring section 

 [Walcott, 1908f, p. 189], 3 mUes (4.8 km.) north of Valcalda Spring and 4 miles (6.4 km.) west-northwest of the Drink- 

 water mine, Silver Peak quadrangle (U. S. Geol. Survey), Esmeralda County, Nevada. 



Micromitra (Paterina) logani (Walcott). 



^ Plate II, figures 6, 6a-b. 



fyhidea logani Walcott, 1897, Proc. U: S. Nat. Mus., vol. 19, pp. 711-712, PL LIX, figs. 2, 2a-b. (Described and 

 discussed essentially as below as a new species. The specimen represented by figs. 2, 2a-b is redrawn in this 

 monograph, PL II, figs. 6, 6a-b.) 



Ventral valve conical, transverse in outhne at the base, almost semicircular. Beak minute, 

 incurving over the pseudodeltidium. Cardinal slopes rounded and flattened so as to form a 

 fairly well-defined false area that is broken by a very wide triangular space. Pseudodeltidium 

 arching upward, forming a narrow, sloping shelf beneath the beak, the angle of slope from the 

 summit of the shell over the beak and pseudodeltidium being nearly the same as the slope from 

 the summit to the fi'ont. 



Surface marked by very fine concentric striae and somewhat coarser Unes of growth. Under 

 a high power sUght traces of radiating strire may be observed. The concentric striae pass around 

 over the false area and cross the pseudodeltidium. Shell substance corneous. 



Observations. — This specimen was received from Whiteaves, of the Geological Survey of 

 Canada, as the type of M. (P.) bella (Bilhngs) . It differed, however, so materially from the 

 description of that species [Billings, 1872b, pp. 477-478] and the figure illustrating it that I 

 found it necessary to give it a distinct specific designation. (See pp. 335 and 345.) 



Tliis species approaches most nearly M. (P.) crenistria (Walcott) in its short pseudodel- 

 tidium and fuiely striated surface. It differs, however, in the character of the surface striae, 

 the form of the false area, and the pseudodeltidium. 



The specimen bears the label "Trois Pistoles, 1S6S, T. C. Weston." It was collected from 

 a bowlder in the conglomerate at that locality, and it is probably of Middle Cambrian age, though 

 this can not be stated positively, as there are no associated fossils. Billings [1872b, p. 478] 

 speaks of the occurrence of fragments of trilobites in the bowlder containing his type of Micro- 

 mitra (Paterina) bella. He does not mention the genera or species. 



