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 



