NO. 1395. CAMBRIAN BR ACHIOPOD A— WALCOTT. 293 



half as long as the width of the shell below; area narrow. Ventral valve with a 

 strongly deiiressed, rather narrow and rounded mesial sinus. Dorsal valve with a 

 narrow, sharply elevated fold not extending quite to the l)eak; side of the valve 

 rounded. Surface smooth in the casts, but jiresenting the ai>pearan<;e of liaving been 

 externally striate. Processes in the interior of the dorsal valve apparently forming 

 a small spoon shaped pit at the beak. 



OhseriKiUons. — Casts of the interior show the form of the spondy- 

 lium and supportino- median septum in the ventral valve; also the 

 small, short spondyliimi in the ventral valve, which appears to be 

 attached to the bottom of the valve without a median septum. 



This species differs from S. harahuensis in its smaller size, less trans- 

 verse outline, and more pronounced mesial depression on the ventral 

 valve. Examples occur of the dorsal valves of the two species that 

 are very similar. Some of the shells approach certain forms of 8. cal- 

 cifera^ but the larger number are less convex and more transverse and 

 with more obtuse cardinal angles. A shell closely allied to S. primor- 

 dialis, and apparently identical, occurs in the Reagan limestone. Only 

 the exterior is known. 



Formation and locality. — Upper Cambrian. St. Croix sandstone, 

 Taylors Falls, Adams County, Wisconsin. Abundantly at Minneiska, 

 and more rarely at River Junction, Houston County, and near Winona, 

 Minnesota. 



Numerous examples of a closely related shell occur in the upper part 

 of the Reagan limestone in the SE. corner, NE. i sec. 2,T. 4 N., R. 

 13 W., 15 miles northwest of Fort Sill, Wichita Mountains, Oklahoma 

 Territory. 



A single ventral valve of the nonplicate shell with a deep sinus 

 comes from the Upper Cambrian, Reagan limestone, Indian Territory, 

 NW. i sec. 1, T. 2 S., R. 1 E. Specimens of the ventral valve of a 

 shell apparently identical with S. i>r!inordlalis occur in the limestone 

 passage beds between the Upper Cambrian and Ordovician on the north 

 side of Tepee Creek, east side of Big Horn Mountains, Wyoming. 



SYNTROPHIA PRIMORDIALIS ARGIA, new variety. 



This specimen is separated as a variety of S-iyriinordialis on account 

 of its less convexity and more shallow median sinus which has three 

 rudimentary plications in it. 



Fonnatlon and loadity. — Upper Cambrian. St. Croix sandstone, 

 Reeds Landing, foot of Lake Pepin, Minnesota. 



SYNTROPHIA ROTUNDATA, new species. 



General form rotund, unequally biconvex; hinge line short. Sur- 

 face marked by fine, concentric striae and low, imbricating varices of 

 growth. The longest shell observed has a width of 18 mm. ; length 

 11 mm. Ventral valve convex at the umbo and beak, but depressed 

 toward the front by a strong, broad, and deep median sinus. Area low, 



