292 THE PALEONTOLOGY OF MINNESOTA. 
{Batostoma varium. 
to each zocecium rising generally from the wall at some point between the angles 
of junction. Many of the latter are occupied by small mesopores, but these are to 
be regarded as comparatively very few and at all times difficult to distinguish 
externally. 
Internal characters: In tangential sections the tubes are polygonal and have 
rather thin walls in which the line of contact between adjoining tubes is distinctly 
preserved. Mesopores few, small, chiefly at the angles of junction. Acanthopores 
small, inconspicuous. In vertical sections the tubes proceed toward the surface in 
a very gentle curve until they enter the unusually narrow peripheral region, where 
the curve is sufficiently accelerated to enable them to open at the surface with 
nearly direct apertures. Diaphragms are very remote or wanting in the axial 
region, and not numerous even in the peripheral portion. Here each tube pre- 
sents from one to five, separated by intervals of from one-half to one tube-diameter. 
In the mesopores, which appear to be very short, the diaphragms are much closer 
with three or four in 0.5mm. In the central part of transverse sections (fig. 14) the 
tubes are conspicuously divided into a large and small set, both having very thin 
walls. 
The large size of the zocecia distinguishes this species not only from all the 
other forms of the genus known but from all the associated bryozoans as well. 
Anolotichia impolita, restricted to the bed of shales immediately beneath (“Stictopo- 
rella beds”), has zocecia fully equalling those of the present species in size, but they 
are each provided with a lunarium and are commonly of either rhomboidal or hexa- 
gonal shape, while the surface is without monticules and the growth of the zoarium 
decidedly irregular. 
Formation and locality.—Four specimens were found in the middle third of the Trenton shales, 
three at Minneapolis, the fourth at West St. Paul. 
BATOSTOMA VARIUM, M. Sp. 
PLATE XXV, FIGS. 16-25. 
Zoarium growing from a large basal attachment into erect branches. These 
vary in width from 7 to 20 mm. but average from 10 to 15 mm., are generally a little 
compressed and divide most irregularly. In some cases the basal expansion consists 
of several distinct layers, varying from 1 to 3 mm. in thickness. Surface without 
monticules, but exhibiting instead clusters of orifices larger than the average and 
separated by interspaces wider than usual. Not infrequently the center of these 
clusters is marked by a small substellate solid macula. Superficial characters 
variable, the walls in some cases being thin, with the zoecial apertures subangular, 
