BRYOZOA. 179 



Stictoporella.] 



segments. The other, apparently the basal or primary segment, is pointed below 

 trifurcately divided 4 mm. above the lower extremity, with the three branches of 

 equal strength and the central one again divided, this time merely bifurcating, at 

 its upper end ; total length 8 mm., width about 10 mm. The zoarial growth and 

 general aspect of the segments seems therefore to be precisely as in A. bifurcata. 



Zoit cial apertures small, subcircular, separated from each other by spaces fully 

 equalling their diameter ; arranged in rather irregular, more or less oblique trans- 

 verse series, about six in 1 mm., and in six to eight, more regular, longitudinal rows, 

 with twelve to fourteen in 3 mm. Immediate border of apertures formed by a ring 

 of very minute granules. This ring is depressed except at the lower end, so that it 

 is not likely to be seen save under the most favorable circumstances. The lower 

 end is commonly prolonged into one or two short rows of granules, perhaps extend- 

 ing completely across the end interspaces. The most striking peculiarity of the 

 species is a horseshoe-shaped ridge, open below, which, in the usual state of preser- 

 vation, appears to enclose the sides and upper end of each zocecial aperture. This 

 ridge is papillose, thick, and strongly elevated in the middle (in front of each aper- 

 ture) gradually tapering to the ends. The strong elevation in front of the apertures, 

 causing them to appear as oblique and turned backward, suggested the name reversa. 

 The ends of the horseshoe ridge may be free, (see fig. 26) or they may unite with the 

 sides of the one next beneath. Non-poriferous border rather wide, with distinct, 

 oblique rows of papillae. 



* 



Formation and locality. Upper third of the Trenton shales, at St. Paul, Minnesota. Recent collec- 

 tions made at this locality from this horizon and the overlying Galena shales afford a considerable number 

 of detached segments agreeing in all essential features with the described types of the species. 



Mits. Reg. No. 8109. 



Genus STICTOPORELLA, Ulrich. 



Stictoporella, ULKICH, 1882, Jour. Cin. Soc. Nat. Hist., vol. v, pp. 152 and 169; and 1890, Geol Surv. 



111., vol. viii, p. 394; VINE, 1884, Fourth Rep. Brit. Assoc. on Foss. 

 Poly., p. 44; MILLEK, 1889, North Amer. Geol. and Pal., p. 325. 



Zoaria bifoliate, growing from a broad basal expansion into narrow, parallel- 

 margined, branching stipes, simple leaf-like fronds, or cribrose expansions. Zocecia 

 with the primitive portion tubular, unusually long, generally without hemisepta, the 

 inferior one only occasionally present. Apertures elliptical, placed at the bottom of 

 a sloping area, the latter usually polygonal. More or less numerous, thick-walleti, 

 untabulated mesopores occur between the zocecial apertures and line the zoarial 

 margins. Maculae, composed of clustered mesopores, and sometimes of zooecial aper- 

 tures of larger size than the average, commonly scattered over the surface of the 

 frondescent species. 



