340 



CAMBRIAN BRACHIOPODA. 



Linnarsson [1876, p. 25] gives the following description of the dorsal valve of this species: 



Shell small, transversely oval, broadest about the middle. Hinge-line straight, shorter than the width of the 

 shell; cardinal angles rounded. Shell substance apparently corneous. Surface marked with numerous sharply 

 marked, concentric lines of growth. Length, 3 mm. ; breadth, 4 mm. 



In some material received from Andrarum, Sweden, I found what appear to be the ventral 

 and dorsal valves of this species associated with Micromitra (IphideUa) ornatella (Linnarsson) 

 and Acrotreta socialis von Seebach. The ventral valve shows a well-defined false area on 

 each side of a triangular opening. The broken edge of the pseudodeltidium is shown on the 

 side of the upper end of the fissure, but its form and depth can not be determuied. 



This species is related to Micromitra (Paterina) labradorica (Billings), differing from it 

 in having a less elevated ventral valve, radiating ridges on the surface, and being more uni- 

 formly smaller in size. It is evidently a rare form, as only three specimens were met with in 

 brealdng up a large quantity of rock. 



Formation AND LOCALITY. — Middle Cambrian: (8w) himestones oi the Paradoxidesforchhammeri zone, at Andra- 

 rum, 20 miles (32.2 km.) northwest of Simi-ishamn, Pro-\ance of Christianstad; (320f) limestone at Andrarum, 20 miles 

 (32.2 km.) northwest of Simrishamn, Province of Christianstad; and (320u [Linnarsson, 1876, p. 25]) strata with 

 Agnostus lievigatus at Ostra Rynninge, in Nerike; all in Sweden. 



(16h) Limestones of the Paradoxides forchhammeri zone at Borregaard; and (16]) limestones of the Paradoxides forch- 

 hammeri zone at LaesaS,; both on Bornholm Island, Denmark. 



Matley [1902, p. 146] has identified this species from the following locality:'^ 



Upper Cambrian: (304b) Lower part of the "White Leaved Oak" shales (the zone of Polyphyma), Malvern Hilla, 

 between Herefordshire and Worcestershire, England. 



/ 



Micromitra scotica n. sp. 

 Text figures 21A-C. 



Ventral valve moderately convex, transverse in outline. Beak almost apical, slightly in 



Cardinal slopes flattened to form a 

 false area that is almost as wide 



advance of the posterior margin, which is nearlj- straight. 





as the greatest width of the shell. 

 Pseudodeltidium narrow and arch- 

 ing somewhat above the 2:)lane of 

 the margin of the shell. 



Dorsal valves unknown. 



Surface marked by rather 

 coai'se concentric striaB and radiat- 

 ing ridges. The concentric striae 

 cross the false area and the pseu- 

 dodeltidium. 



Ohservations. — This species ap- 

 pears to be most closely related to 



Figure 21.— Micromitra seolkan. sp. A, Type specimen, a ventral valve, X4, from Local- MicrOmitra, "pUSiJlcL (LiunarSSOn), 



ity 316d, Lower Cambrian shale on Meall 4 Ghiubhais, Ross-shire, Scotland (U. S. ,,.,i I'f 'l If +I-1 + 



Nat. Mus. Cat. No. 68310). B,B', B", Top, side, and back views of a ventral valve, X-5, ^^'t IS tO DC aiStmgUlSnea trom mat 



froraLoc^litySied, Lower Cambrian shale on Meall ^ Ghiubhais, Ross-shire, Scotland sDGcieS bv rCaSOn of its loU^ PSeU- 



(Geol. Survey Scotland, specimen No. M2046e). C, Top view of a crushed ventral 1 , i, -j-" -1,-1 e i iU i il, 



valve, X2.5, from Locality 316d, on Meall 4 Ghiubhais, Ross-shire, Scotland (Geol. Ciodeltldium and tile lact that the 



Survey Scotland, specimen No. M«78d). |^p^|. ^^^^ ^^^^ overhang the falsC 



area. The latter species occurs in the Middle Cambrian and Micromitra scotica is associated 

 with Olenellus in Scotland. 



Formation and locality.— Lower Cambrian : (316d) 6 Localities M2646e, M2647e, and M4178d of the Geological 

 Survey of Scotland, about 500 feet (152.5 m.) above the provisional base of the Cambrian and 75 feet (23 m.) below 

 what is believed to be the top of the Lower Cambrian in the shales forming 5 and 6 of the section given by Peach and 

 Home [1907, p. 414], in a small burn on the north slope of Meall & Ghiubhais, 4 miles (6.4 km.) west-northwest of the 

 Kinlochewe Hotel, Loch Maree, Ross-shire, Scotland. 



o Groom (1902, p. 109] describes the locality and cites a list of the associated species. 



6 Specimens from this locality are also included m the collections of the United States National Museum. 



