178 THE PALEONTOLOGY OF MINNESOTA. 



[Anthropora. 



In figures 21 a, ft, c, I have endeavored to show all the characters of the zocecia 

 that are to be brought out in tangential sections. The right sides of a and ft repre- 

 sent the structure just beneath the surface, while the left sides show it at a deeper 

 level in the section. In 21 c only the primitive or prostrate portion of the zooecia is 

 shown. 



The unbranched character of the segments of this species, as well as their greater 

 length, will distinguish them at once from all other species of the genus, 



Formation and locality. Very abundant in the lower and middle thirds of the Trenton shales, at 

 Minneapolis, St. Paul, Fountain and other localities in Minnesota; Decorah, Iowa. 



Mus. Reg. Nos. 5933, 8075. 



ANTHROPORA BIFURCATA n. sp. 



PLATE XIV, FIGS. 23-25. 



Segments small, thin, with sharp edges and rather wide non-poriferous border, 

 the lower ones bifurcating, usually only once ; so far as observed not over 8 mm. 

 long, and from 1.2 to 1.8 mm. wide; the upper joints shorter, their length occa- 

 sionally less than 5 mm., bifurcating, or with a single lobe-like projection on one or 

 both sides. Young segments with comparatively large, ovate zocccial apertures, not 

 very regularly arranged in longitudinal and diagonally intersecting series, with 

 about nine in 3 mm. lengthwise, and five in 1 mm. diagonally. Apertures enclosed 

 in distinct granulose rims, connecting longitudinally. Interspaces depressed, some- 

 times with a few indistinct strias. With age the zooecial apertures become more 

 circular and smaller, and the peristomes and connecting ridges thicker. 



This species is related to A. shafferi (Meek) but differs in having only one ridge 

 or line in the interspaces, instead of from one to four. A. simplex has longer and 

 unbranched segments, while A. reversa has a peculiar horseshoe-shaped ridge about 

 its zoo3cial apertures. 



Formation and locality. Detached segments rather common in the Galena shales and in the upper 

 third of the Trenton shales at St. Paul, and Cannon Falls, Minnesota. A closely allied species, perhaps it 

 is identical, in the Trenton limestone of Kentucky, Tennessee, and Canada. 



Mvs. Reg. No. 8108. 



ARTHROPORA REVERSA n. sp. 



PLATE XIV, FIG. 26. 



Of this species I have seen only two segments, but their superficial aspect is so 

 distinctive that I do not hesitate in proposing a new name for them. One of these 

 is 8 mm. long, and divides dichotomously about midway the length. The two forks 

 are of the same strength as the lower half, averaging 1.2 mm. wide, the three 

 extremities abrupt and tipped for articulation with the preceding and succeeding 



