182 THE PALEONTOLOGY OF MINNESOTA. 



LStictoporella. 



and more abundant mesopores. The occasional inosculation of the branches points 

 to a relationship with S. cribrosa, and this is further evidenced by the agreement in 

 their internal structure. The position of the species is probably intermediate between 

 S. angularis and S. cribrosa. 



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

 Mus. Reg. No. 8110. 



STICTOPORELLA ANGULARIS Ulrich. 



PLATE XI, FIGS. 1-3, 6, and 8-11. 



Stictoporella angularis ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 71. 



Zoarium branching dichotomously at intervals varying from 4 to 10mm.; branches 

 more or less compressed, 1.5 to 3.0 mm. wide, 0.7 to 2.0 mm. thick, with sharp or nar- 

 rowly rounded, subparallel edges. Zooscial apertures small, subcircular, set into wide 

 sloping polygonal areas, with the subrhomboidal and hexagonal shapes commonest. 

 Walls ridge-shaped, angular in the middle, their thickness usually greater than the 

 diameter of the apertures. Zooecial .apertures arranged in moderately regular 

 curved diagonally intersecting series, nine in 2.5 mm. When longitudinal rows are 

 to be made out (as in upper part of fig. 6) six are to be counted in the same space 

 lengthwise. Mesopores comparatively few, small, sometimes appearing to be absent 

 entirely on parts of the central three-fifths of the surface, while for some distance 

 above or beneath such a spot they may occur regularly one to each zocecium. Near 

 the margins, however, some are always present, with one and occasonally two rows 

 bordering the edges. 



In tangential sections, showing the structure in the peripheral part of the zoa- 

 rium, the zoo3cial cavity is ovate, in old examples sometimes nearly closed by inter- 

 nal deposits of sclerenchyma, the interspaces always thick enough to separate the 

 cells by a distance greater than their diameter. Boundary line between the zorecia 

 and mesopores sharply defined, consisting of a crowded row of very minute, pore-like 

 dots. These, however, are not recognizable except in the most favorably preserved 

 specimens. Mesopores few, here completely filled with laminated sclerenchyma. 



In vertical sections the thin-walled prostrate part of the zocecial tube is long, 

 but, as is usual in this genus, this portion of the section appears irregular. Hemi- 

 septa absent. In turning to the surface the tube bends abruptly, and at once the 

 walls become very thick and marked with A-shaped lines representing the sloping 

 areas about the apertures at previous stages of growth. 



The angularity of the zooecia, together with the unusual paucity of the meso- 

 pores, distinguishes this species from S. interstincta, S. riyida, S. dumosa and S. cribrosa. 



