360 CAMBRIAN BRACHIOPODA. 



TMs form owes its specific name to its occurrence on the shores of Lake Ijouise. 

 Formation and locality. — lower Cambrian: (35d) About 3,150 feet (960.1 m.) below the Middle Cambrian in 

 the siliceous Lake Louise shale [^^alcott, 190Sf, p. 216] in cliff on the north side of Lake Louise, at its upper end, 

 southeast of Laggan on the Canadian Pacific Railway, Alberta, Canada. 



MtcROMiTRA (Iphidella) nyssa Walcott. 

 Plate III, figures 9, 9a. 



Micromitra (Iphidella) nyssa Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 57, PI. VII, fig. 5. (Described 

 and discussed as below as a new species. Fig. 5 is copied in this monograph, PI. Ill, fig. 9.) 



Ventral valve subcircular in outline, with the posterior margin almost transverse ;' form 

 depressed, conical, with a minute beak incurving over the pseudodeltidium. The cardinal slope 

 is compressed in all the specimens, but it indicates that there was an imperfectly defined 

 narrow area. Pseudodeltidium, as far as can be determined, broad and short, with its lower 

 margin broadly arched. Dorsal valve shghtly convex, beak marginal. No traces of a false 

 area or pseudodeltidium have been observed. 



Surface marked by concentric strise and lines of growth that are crossed obhquety by two 

 sets of fine elevated line's. The crossing of the latter lines forms minute, shallow, rhomboidal 

 pits, which give to the surface the appearance of a fine network. On the ventral valve the 

 striae cross the pseudodeltidium. Shell substance corneous. 



Ohservations. — This is one of the largest shells of this genus. The ventral valve has a length 

 of 11 mm., width 13 mm. In form it resembles Micromitra (Paterina) lahradorica (BilUngs) 

 and in surface characters M. (Iphidella) ^ omatella (Linnarsson) and some varieties of M. (I.) 

 pannula (Wliite). 



Formation and locality. — Middle Cambrian: (iq) About 315 feet (96 m.) above the unconformable base of the 

 Cambrian and 190 feet (57.9 m.) above the top of the quartzitic sandstones, in a shale which corresponds in strati- 

 graphic position to the upper part of shale No. 6 [see 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. 



Micromitra (Iphidella) ornatella (Linnarsson). 



Plate III, figures 6, 6a-d. 



Iphidea ornatella Linnarsson, 1876, Bihang till K. svensk. Vet.-Akad. Handl., Bd. 3, No. 12, pp. 2.5-26, PI. Ill, figs. 



42a-e, 43a-c. (Described and discussed in English as a new species; see below for copy.) 

 Iphidea ornatella Linnarsson, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 97-98. 



(Mentioned in discussion of genus Iphidea.) 

 Iphidea ornatella Linnarsson, GrQnwall, 1902, Danmarks Geol. Unders^gelse, Rsekke 2, No. 13, p. 40. (Mentioned 



in Swedish.) 



The original description by Linnarsson follows: 



Shell small, transversely oval; sides and front rounded; hinge line straight, or nearly so, shorter than the width 

 of the shell; cardinal angles rounded. Surface marked with retiform eminences, including small excavations. The 

 eminences often swell out and become higher at the crossing points, thereby giving to the sm-face a somewhat granu- 

 lated appearance (as in fig. 43). In some specimens there are also more or less distinct radiating ridges, especially 

 near the median line of the shell. The shell substance is apparently corneous, but I have not been able to discern 

 more than one layer. 



The color in the specimens from Bornholm is black, in those from Westrogothia more brown. Ventral valve 

 convex, subconical. Beak erect and pointed, pierced by a minute round foramen. The posterior, visible only in 

 one specimen, is truncated, so as to form a false area, which has in the middle a triangular fissure, arched over, in 

 the upper part only, by a convex pseudodeltidium. Dorsal valve less convex, somewhat fiattened along the middle; 

 greatest height at the beak, which is not, however, so prominent as in the opposite valve. Hinge area not visible in 

 any of the specimens. Interior of both valves unknown. Two specimens measured : Length 3 mm., breadth 4 mm.; 

 and length 2 mm., breadth 3 mm. 



Linnarsson [1876, p. 26] speaks of the presence of a minute foramen, but after the study 

 of several fuiely preserved ventral valves from the Paradoxides zone of Andraiiim, Sweden, 

 I am led to beheve that what he considered to be an apical foramen is the minute longitudinal 



