PATERINIDiE. 337 



At Ophir, in the Oquirrh Range, it is at the horizon of the Pioche fauna, or near the base of 

 the Middle Cambrian. 



The table in the introduction gives a summary of the numbers and the range of the genus 

 by species and varieties. (See p. 99.) 



MiCROMITRA ALABAMAENSIS (Walcott). 

 Plate II, figures 5, 5a-c. 



Iphidea alabamaensis Walcott, 1897, Proc. U.S. Nat. Mus., vol, 19, pp. 713-714, PI. LIX, figs. 5, 5a-b. (Discussed 

 somewhat as below as a new species. The specimens represented by figs. 5, 5a-b are redrawn in this monograph 

 PI. II, figs. 5, 5a, and 5c, respectively.) 



In following the Lower Cambrian rocks southward from Vermont, the first type of 

 Mieromitra met with is M. stissingensis (Dwight), which occurs in the Middle Cambrian of 

 Dutchess County, New York. This is fairly well distinguished by its surface character from 

 Mieromitra (Paterina) lahradorica (Billings) and its variety swantonensis (Walcott), but at the 

 next locality to the south in eastern Tennessee, 4 miles (6.4 km.) north of Rogersville, in the 

 Rogersville shale of the Middle Cambrian, was found a form that is practically identical with 

 the northern species or its variety, so far as it is possible to compare specimens preserved in 

 limestone with those preserved in shale. A species of the same general form also occurs in the 

 Middle Cambrian shales of the Cowan Creek section, Cherokee County, Alabama. There is, 

 however, a difference in the surface strise that distinguishes it from M. (P.) lahradorica, M. (P.) 

 lahradorica swantonensis, and M. (P.) stissingensis. It is the tendency to crenulation of the 

 strise in nearly all the specimens that have been examined. This, in extreme cases, goes so 

 far as to approach the surface so characteristic of Mieromitra (Iphidella) pannula (White). 

 The form can not well be identified with the closely related M. (P.) lahradorica (Billings) or its 

 variety swantonensis (Walcbtt) or M. (P.) stissingensis (Dwight) on account of these pecuhar 

 surface characters, and the name M. alabamaensis was proposed for it. 



In the general form of the valves this species resembles M. (P.) lahradorica and M. (P.) 

 stissingensis. So far as known the only specific difference is in the surface character, which 

 allies it with Mieromitra sculptilis (Meek) . The convexity of the valves is unknown, owiag to 

 the compressioii of the shells in the shale, and we have no information of the area or pseudo- 

 deltidium. Shell substance corneous. 



Formation and locality. — Upper Cambrian: (94o) Limestone at base of dolomite, 0.25 mile (0.4 km.) beyond 

 Givens Ford, Cowan Creek, about 8 miles (12.8 km.) southeast of Center, Cherokee County, Alabama. 



Middle Cambrian : (90x and 94a) In and attached to the outer surface of siliceous nodules in the Conasauga ("Coosa ") 

 shale, Coosa Valley, east of Center; (95a) shales on Spring Creek, near the old tram crossing north of Center road. Cowan 

 Creek valley, southeast of Center; and (94) shales 0.25 mile {0.4 km.) beyond Steel Ford, Cowan Creek, about 8 "miles 

 {12. S km.) southeast of Center; all in Cherokee County, Alabama. 



(121a) Shales on road leading from southeast of Harlan Knob to Amis post office; (1S4) shales (NoHchucky?) 

 overlying the limestone which rests on the Rogersville shale, on Big Creek, southeast of Harlan Knob; (123) upper 

 part of Maryville limestone, on Big Creek, southeast of Harlan Knob; and (121) Rogersville shale, road just east of 

 Harlan Knob; all about 4 miles (6.4 km.) northeast of Rogersville [Keith, 1905, p. 4, and areal geology sheet], Hawkins 

 County, Tennessee. 



(14a) Sandstone of the Rome formation, along First Creek Gap, 4 miles (6.4 km.) north-northeast of Knoxville 

 [Keith, 1905, areal geology sheet], Knox County, Tennessee. 



MiCROMITKA HAYDENI Walcott. 

 Text figures 20A-D, page 338. 



MicromitrahaydeniWAhcOTT, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, pp. 55-56, PL VII, figs. Sand 3a. (Described 



and discussed as below as a new species. Figs. 3 and 3a are copied in this monograph as figs. 20A and 20B'.) 



Ventral valve subconical, with a minute beak arching slightly over a strong, arched pseudo- 



deltidium which is about one-half as long as the height of the valve. Cardinal slope rounded; 



a slight angle is indicated by a line where the concentric surface striae bend inward toward the 



pseudodeltidium across the narrow area; a sharp angle is formed where the convex pseudodeltid- 



ium rises abruptly from the area. 



62667°— vol 51, pt 1—12 22 



