356 CAMBRIAN BRACHIOPODA. 



Surface with rather strong concentric striae, and a few somewhat obscure lines of growth. 

 On the ventral valve the strise extend around to and cross the pseudodeltidium. Shell sub- 

 stance corneous. 



Observations. — This is one of the larger species of the genus, being surpassed in size only 

 bj' Micromitra (Paterina) labradorica (Billings). It is clearly distinguishable from M. (P.) 

 iella (BilUngs) by its larger size, more depressed ventral valve, and the form of the pseudo- 

 deltidium. The dorsal valves of the two species are quite similar. It differs from M. fealei 

 (Walcott) in its broad pseudodeltidium, false area, and surface markings. 



One specimen has a length of 9 mm. and a little greater width. The area is vertical, the 

 pseudodeltidium being broken away. 



This species is represented by some fine specimens that occur in the lower part of the 

 Middle Cambrian of northern Utah. Micromitra (Iphidella) pannula (White) occurs 54 feet 

 (16.5 m.) lower in the section and M. {Paterina) stuarti Walcott 16 feet (4.5 m.) higher up.> 



Formation and locality. — Middle Cambrian: (74) Sandstone about 300 feet (91.4 m.) above the base of the 

 Tonto group, at the head of Nunkoweap Valley; (74d) sandstone beds in "Tonto" shale, just above massive sandstones 

 near mouth of Bass Canyon, on the south side of the Grand Canyon; and (73a) "Tonto" sandstone in Chuar Valley; 

 all in the Grand Canyon of the Colorado, Arizona. 



(54n) About 550 feet (167.6 m.) above the Brigham quartzite and 3,640 feet (1,109.5 m.) below the Upper Cam- 

 brian in the limestone forming 2e of the Ute limestone; (54p) about 525 feet (160 m.) above the Brigham quartzite 

 and 3,665 feet (1,127.1 m.) below the Upper Cambrian in the shale forming 2f of the Ute limestone; and (54y) about 

 510 feet (155.4 m.) above the Brigham quartzite and 3,680 feet (1,121.7 m.) below the Upper Cambrian in the lime- 

 stones forming 2g of the Ute limestone; all in Blacksmith Fork Canyon [Walcott, 1908f, p. 197], about 10 miles (16.1 

 km.) east of Hyrum, Cache County, Utah. 



(8j) About 575 feet (175.3 m.) above the unconformable base of the Cambrian in a shale which corresponds in 

 position to shale No. 4 of the Dearborn Kiver section [Walcott, 1908f , p. 202], on the ridge between Gordon and Youngs 

 creeks, about halfway between Gordon Mountain and Cardinal Peak, Ovando quadrangle (U. S. Geol. Survey), 

 Powell County, Montana. 



Specimens that are somewhat doubtfully identified with this species occur in the following 

 locality : 



Upper Cambrian: (160) Sandstones forming a remnant of the Gallatin formation, which lies between the expo- 

 sures of "porphyrite" on the east side of Willow Creek [Peale, 1896, areal geology sheet]. 12 miles (19.2 km.) south- 

 Bouthwest of Threeforks, Threeforks quadrangle (U. S. Geol. Survey), Gallatin County, Montana. 



Micromitra (Paterina) undosa (Moberg). 



Text figures 28A-C. 



Kutorgina undosa Moberg, 1892, Geol. Foren. i Stockholm Forhandl. for 1892, Bd. 14, Hft. 2, p. 112, PI. Ill, figs. 

 10-12. (Described in Swedish as a new species; see below for free translation. Figs. 10-12 are copied in this 

 monograph as figs. 28C, 28A, and 28B, respectively.) 



Moberg describes this form essentially as follows: 



No specimen shows the umbonal part of the ventral shell completely preserved, yet it seems as if the umbo had 

 -projected somewhat beyond the straight hinge margin. From the umbo the shell slopes gently in all directions, 



forming a rather feebly convex surface with even arch. The dorsal 

 valve is more flattened and less evenly arched than the ventral 

 and more transverse, with the anterior corners evenly rounded off. 

 The area is not quite distinctly preserved on any specimen; the 

 ^. beak is situated quite near the posterior edge; it is sharply marked 



„„ ,,■ : ,1, , ■ ^ ;, /»f.,K.>™^ J Tj and projects with a somewhat blunt point. The ornamentation of 

 TiGXTR-E 28.— Micromitra (Palmna) undosa (Uoherg). A, B, r J _ r , , ,. , ^, 



Ventral valves. C , Dorsal valve. the shell IS very characteristic ; the strongly marked Imes of growth 



The specimens represented by figures 28A and 2SB are appear to be formed of a row of small bows, and on some specimens 



from Locality 390a, drift blocks of Lower Cambrian sandstone there are fine, short, sharp, radiating, subordinate, depressed lines, 



at Stora Ror, Oeland Island; tliat represented by figure 28C fj^g gj^gj] jg quite thick, and, it is thought, formed of a hornlike 



is from Locality 390h, drift blocks of Lower Cambrian sand- ,,,v,„t„i,f,p 

 .stone on Nordmannaskar Island; both in Sweden. Figures 



rdfo^%i;S^aXilS ^'- "pr'estting'tbe Two specimens of medium size are 4 mm. and 3.5 



type specimen. mm. long and 5 mm. and 4.75 mm. broad, respectively. 



Judging by the fragments the species must have attained considerable size. 



