BRYOZOA.. 291 
Batostoma magnopora.] 
Internal characters: In vertical sections the tubes have thin and somewhat 
irregularly fluctuating walls in the axial region. Their course to the surface is 
gently curved throughout, and as they near the same their walls are appreciably 
thickened, while mesopores, whose number varies greatly in different specimens, are 
abruptly developed. The mesopores may be constricted at the points where they 
are intersected by the diaphragms. The latter are often thickened circumferentially, 
and vary somewhat in the number occurring in a given space, seven and eleven in 
1 mm. being the extremes so far noticed. In the axial region diaphragms are very 
far apart or are wanting entirely, but in the peripheral portion the average distance 
between them is about equal to half their diameter. Specimens more than 12 mm. 
thick consist of two or more layers of tubes. 
The four tangential sections figured on plate XXV, fully illustrate the charac- 
ters of the species as brought out in this kind of section. Fig. 7 is from a specimen 
with very thin walls, few mesopores, and scarcely distinguishable acanthopores, the 
latter being in the angles of junction. Fig. 4 represents a small portion of a section 
prepared from the original of fig.2. In this, which is an average example, the walls 
are thicker, mesopores more abundant, and the acanthopores, though small, more 
readily distinguished. Minute foramina are shown in the diaphragms of some of the 
mesopores. Figures 8 and 9 are from specimens of the variety circulare, the first 
with thick zocecial walls, the second with them thin as in fig. 6. 
In a general way this species reminds one more of upper Hudson river species 
than of Trenton forms. Variety circulare resembles B. manitobense Ulrich,* very 
closely, but the clusters of large zocecia are more conspicuous in that species. The 
typical variety on the other hand is more like B. variabile, differing from it chiefly 
in the smaller size of the acanthopores. Compared with associated Bryozoa none 
save Anolotichia impolita have as large zocecia. 
Formation and locality—Abundant in the lower third of the Trenton shales at Minneapolis and 
St. Paul, Minnesota. 
Mus. Reg. No. 8136; var. circulare, 8137. 
BaTOSTOMA MAGNOPORA, 2. Sp. 
PLATE XXV, FIGS. 12-15. 
Zoarium ramose; branches large, subcylindrical, 8 to 15 mm. wide; surface 
elevated at irregular intervals into low monticules, the latter broad and occupied 
by zowcia a little larger than the average. Zocecia unusually large, about eight in 3 
mm., their apertures polygonal, the walls thin, with one or two small acanthopores 
*Contr, Micro-Pal. Cambro-Sil. rocks of Canada, pt. II, p. 33, 1889. 
