BRYOZOA. 297 
Batostoma minnesotense. ] 
BAaTosTOMA MINNESOTENSE, 7”. Sp. 
PLATE XXVI, FIGS. 38-40; PLATE XXVII, FIGS, 9-15. 
Amplexopora superba ULRICH, 1886. Fourteenth Ann. Rep. Geol. Nat. Hist. Surv. Minn., p. 92. 
(Not Foord, 1883, Contri. Micro-Pal. Cambro-Sil. Rocks, Can., p. 16.) 
Zoarium ramose, above the medium size for the genus; branches without mon- 
ticules, subcylindrical, bifureating at rather long intervals, averaging 9 or 10 mm. 
in diameter, but varying between the extremes of 7 and 15mm. Zocecial apertures 
subangular, with walls of moderate thickness, arranged in regular curving series 
about clusters of orifices that are in most cases decidedly larger than the average; 
of the latter sometimes nine, more often ten, occur in38 mm. Prominent acantho- 
pores at all the angles of junction, and in many cases another is placed between the 
angles. These at all times occupy the summit or center of the walls and in no case 
cause irregularities in the form of the zocecial apertures. Mesopores very few, 
scattered at random among the larger apertures. 
Internal characters: In tangential sections the walls are nearly uniformly thick, 
with the angles of junction often appearing as open (pl. XXVII, fig. 15). In other 
cases the angles are occupied by dark spaces looking more like the usual appearance 
of acanthopores. A more typical phase of the species is shown in figs. 9 and 10, 
representing parts of a section of an excellently preserved example. In this we 
have more abundant acanthopores and the cavity in these is unusually large, while 
many of the angles are occupied by open spaces similar to those shown in fig. 15. 
In vertical sections the tubes are provided with thin wavy walls in the axial 
region, where they are also a little irregular and generally entirely without dia- 
phragms, the latter first making their appearance as the tubes bend into the 
peripheral region. In the outer region the walls are much thickened and in places 
distinctly traversed longitudinally by acanthopores. The mesopores are but seldom 
observed, have few diaphragms and appear to be in part filled with solid tissue. The 
arrangement of the diaphragms in the zocecial tubes varies somewhat in different 
sections. Figures 11 and 13 represent extremes in this respect. 
This species, though closely related to B. winchelli, is readily distinguished 
externally by its larger size and slightly larger and more regularly arranged zocecial 
apertures; internally by the wavy walls and the absence of diaphragms in the axial 
region. Foord’s Amplexopora superba, to which I at first referred this species, is 
probably congeneric, but distinguished specifically by having nearly straight instead 
of wavy walls to the axial tubes, and a tuberculated surface. 
Formation and locality.—Not rare in the middle third of the Trenton shales at Minneapolis, St. 
Paul and other localities in Minnesota. 
Mus. Reg. Nos. 5996, 5998, 7592, 7668, 8093. 
