366 THE PALEONTOLOGY OP MINNESOTA. 



[Sohizotreta rainutula. 



thirteen to fifteen in the space of 2 mm. Dorsal valve depressed-convex. Ventral 

 valve strongly elevated at the apex, perforate; posterior slope rapid, convex; anterior 

 slope flat, or slightly concave. Pedicle opening short, narrow, oval and surrounded 

 by an elevated margin. In the interior, on each side of the pedicle area, are situated 

 the very narrow posterior adductor scars. The margin of this valve is distinctly, 

 but slightly reflexed, producing a broad, shallow groove along the outer margin of 

 the natural casts. 



This species differs from Discina circe Billings^ -Orbiculoidea lamellosa Hall, in 

 having the ventral valve more elevated, while in the latter it is the shallower valve 

 that has the pedicle opening. The apices of the valves also are much more excentric 

 in S. pelopea than they are are in Hall's species, being very nearly central in the 

 latter. From Schizotreta conica Dwight, and S. ovalis Hall, it differs in being in outline 

 and not narrowly oval. 



Formation and locality. Not uncommon in the Galena limestone, just above the Galena shales, 

 in the quarries at Mantorville and at Old Concord, Minnesota. Also from the same formation at 

 Dubuque, Iowa, and Neenah, Wisconsin. From the Salmon Kiver (Hudson River) formation at Spring 

 Valley, Minnesota. Also in the Trenton limestone at Montreal, Canada. 



Collectors. A. D. Meeds and the authors. 

 Mus. Beg. Nos. 263, 296, 7688-7690. 



SCHIZOTRETA MINUTULA, n. sp. 

 a bed 



FIG. 28. a, dorsal valve; b, ventral valve; c, profile view; d, interior of dorsal valve; all x 18. 



Description: Shell minute, nearly circular in outline, marked by numerous, 

 delicate concentric lines of growth and sometimes a few radii, in the anterior 

 region; valves about equally convex. Ventral valve with a minute circular pedicle 

 opening in the apex of the shell. Area posterior to the dorsal beak more excavated 

 than that of the other valve. 



Interior of the dorsal (?) valve apparently with two pairs of muscle scars, the 

 posterior pair the larger, diverging forward and situated one on each side of the beak 

 cavity; the other pair is placed medially near the lateral margin. 



Dimensions, iV of a millimeter in length. 



This little species is the smallest adult brachiopod from paleozoic rocks known. 

 Individuals occur in abundance associated with stems of Diplograptus, to which they 

 were probably attached. This may account for their small size. 



Formation and locality .From the lower portion of the Hudson River group near Granger, Minnesota, 

 Mus. Reg. No. 8392. 



