354 CAMBEIAN BRACHIOPODA. 



observed, but appear at irregular intervals singly or in groups; while apt to be crowded around the beak, they are 

 rare near the front margin. On the best specimens about 25 have been counted in the central part of the shell just 

 forward of the beak; had they extended in equal distribution around it, quite to the cardinal border, there would 

 have been about 50. They are also unequal in breadth; where they are somewhat regular, the interspaces about 

 equal the plications in width; these plications are multiplied by implantation. 



Observations. — Some young specimens show a surface ornamentation very much hke that 

 of Micromitra sculptilis (Meek) (PI. Ill), but the ornamentation of tlie adult shell is quite 

 distinct. As stated by Dwight [1889, p. 147], fragments of the shell in the shale might be 

 taken for the shell of "Lingulepis pinniformis" (see Lingulella (Lingulepis) acuminata (Con- 

 rad), p. 545). He also calls attention to the general resemblance to Micromitra (JPaterina) 

 lahradorica (Billiags). 



Attention has been called under the description of M. alahamaensis (Walcott) (p. 337) to 

 the similarity of form and surface ornamentation between that species, M. (P.) lahradorica 

 (Billings), M. (P.) lahradorica swantonensis (Walcott), and M. (P.) stissingensis. 



An apparently identical form occurs at Mount Stephen, British Columbia, in association 

 with Ogygopsis Tdotzi (Rominger). It has the same outline and shows the variations of surface 

 ornamentation so characteristic of M. (P.) stissingensis (Dwight) from New York. The radial 

 markiags are lightly impressed and are so often entirely obscured that the Mount Stephen 

 form frequently resembles the form described under the name of Micromitra zenohia (p. 342). 



This forna owes its specific name to its occurrence near Stissing, New York. 



Formation and locality. — Middle Cambrian: (367d [Dwight, 1889, p. 145]) Limestone near Stissing, Dutchess 

 County, New York. 



A single specimen of a dorsal valve 3 mm. in width, that is apparently identical with shells 

 of similar size from the tj^pe locality, occurs at the following locaUty: 



Middle Cambrian: (11m) Drill cores of limestone in the Bonneterre limestone at horizons 10 and 20 feet (3 and 

 6 m.) above the Lamotte sandstone, St. Francois County, Missouri. 



Apparently identical forms occur at the following locality: 



Middle Cambrian: (14s) About 2,300 feet (701 m.) above the Lower Cambrian and 2,700 feet (823 m.) below the 

 Upper Cambrian, in the Ogygopsis zone of the Stephen formation [Walcott, 1908f, p. 210], at the "fossil bed" on the 

 northwest slope of Mount Stephen, above Field, on the Canadian Pacific Kailway, British Columbia. 



{/ Micromitra (Paterina) stissingensis ora n. var. 



This form is distinguished from the specimens tentatively referred to Micromitra {Paterina) 

 stissingensis on Mount Stephen and from the typical specimens of the latter species in New 

 York by its uniformly larger size and in its distinct radial striation. The Mount Stephen 

 representatives of M. (P.) stissingensis frequently betray so little evidence of radial striation 

 that they resemble Micromitra zenohia, a form which is associated with M. (P.) stissingensis 

 ora and which differs from the latter variety in the entire absence of radial striation. It is 

 possible that the Canadian forms will prove to be distinct from the New York species. Nothing 

 is known of the cardinal area or pseudodeltidium of M. (P.) stissingensis ora. 



Formation and locality. — Middle Cambrian: (35k) Shales in the Stephen formation on the west slope of the 

 ridge between Mount Field and Wapta Peak, 1 mile (1.6 km.) northeast of Burgess Pass, above Field, British Columbia. 



Micromitra (Paterina) stuarti Walcott. 



Text figures 26A-B, page 355. 



Micromitra (Paterina) stuarti Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 58, PL VII, figs. 8 and 8a. 

 (Described and discussed as below as a new species. Figs. 8 and 8a are copied on page 355, figs. 26A and 26A'", 

 respectively.) 



Ventral valve subcorneal, mth a minute beak arching slightly over a short pseudodeltidium. 

 Cardinal slope with a rounded angle that extends from the beak to the posterolateral margin 

 and defines a. very narrow, flattened area on each side of a high triangular fissure that is covered 

 for a short distance at the top by a very short, arched pseudodeltidium. 



