302 THE PALEONTOLOGY OF MINNESOTA. 
[Stromatotrypa ovata. 
Apertures oval, separated by depressed interspaces, the peristomes minutely papil- 
lose. Mesopores abundant, beginning on the basal lamina, decreasing in size with 
age, closely tabulated, the diaphragms finely punctured; mouths rarely visible, 
closed by a common dermal sheet. True acanthopores wanting. 
Type: Stromatotrypa ovata, n. sp. 
The species upon which this genus is based has much to remind us of the 
Devonian Pinacotrypa, Ulrich. But as that genus is clearly a branch of the Fistuli- 
poride, and Stromatotrypa most likely not far removed from Batostoma and T'remato- 
pora, it is evident that there can be no real affinity with Pinacotrypa. The 
arrangement with the Diplotrypide, though provisional, is strongly suggested by 
the dimorphic character of the zoarium and the supposed relationship to Bastos- 
toma. 
STROMATOTRYPA OVATA, %. Sp. 
PLATE XXIV, FIGS. 24-31. 
Zoarium consisting of one or more exceedingly thin layers, varying in thickness 
from 0.5 to 2.0 mm., occasionally attached to shells, but more commonly encrusting 
other Bryozoa. Sometimes the attachment is incomplete, and in a few cases the 
zoarium is free, with the underside wrinkled. Surface without monticules, but 
exhibiting at irregular intervals smooth spots of greater or less extent on which 
the zocecia are generally farther apart than usual and the apertures of some of them 
closed. Zocecial apertures oval, peristomes thin, in contact at limited points or more 
or less widely separated, the arrangement inclining to be irregular, with six to eight, 
commonly seven, in 8 mm.; length of apertures varying from 0.3 to 0.45 mm., the 
average about 0.28 by 0.38 mm. Interspaces depressed, of variable width, apparently 
smooth in the youngest stages, minutely granulose in the aged conditions. Small 
acanthopore-like elevations generally where peristomes come into contact. The 
best preserved specimens exhibit also a row of minute papillee crowning the peri- 
stomes. 
Internal characters: In tangential sections the zoccial walls are thin and in 
contact at one or more points, or they may be completely isolated by mesopores 
varying considerably in shape and size. Attached to the walls, or more frequently 
occupying the angles of junction, are minute rounded and thin-walled cells that are 
perhaps to be regarded as peculiarly modified acanthopores. Good sections show 
besides a large number of smaller dots in the interspaces and zocecial walls. In 
vertical sections both sets of tubes rise abruptly from the basal lamina, and the 
mesopores decrease more or less conspicuously in size in nearing the surface. 
