286 THE PALEONTOLOGY OF MINNESOTA. 
[Diplotrypa limitaris. 
DIPLOTRYPA LIMITARIS, ”. Sp. 
‘a 
LL 
Fig. 18. Diplotrypa limitaris Ulrich, upper beds of the Galena shales, Goodhue county, Minnesota. 
Collection of E. O. Ulrich. Transverse and vertical sections, x 18, showing the tabulation of the tubes 
and the great reduction in the number of mesopores characterizing the species. 
Zoarium, as seen in four specimens, small, hemispherical, 12 mm. or less in diam- 
eter, and 3 to7 mm. in hight. Under surface concentrically wrinkled ; upper surface 
without monticules but presenting rather conspicuous clusters of large cells among 
which the mesopores are commonly more numerous than elsewhere. Walls very 
thin; zocecial apertures polygonal, 0.25 to 0.4 mm. in diameter, with ten to twelve 
in 3mm. Mesopores of variable size, not as numerous as the zocecia. ‘Tabulation 
of tubes comparatively regular and uniform; in the mesopores there are nine or ten 
diphragms in 0.5 mm., in the zocecial tubes six to nine in] mm. As shown at the 
margin of the vertical section figured above, the tabulation of the mesopores changes 
suddenly (? always) into that of the zocecia. 
The unusually small number of mesopores distinguishes this species from D. 
petropolitana and D. westoni (Ulrich). In those species the zocecia are also some- 
what larger, and the tabulation less uniform. 
Compared with associated and other discoidal Bryozoa, the species of Mesotrypa 
are separated by their rounded zocecia and much more abundant mesopores, those 
of Prasopora by the cystiphragms, those of Leptotrypa by their acanthopores, while 
those of Monotrypa are entirely without mesopores. 
Formation and locality.—Upper beds of the Galena shales at localities in Goodhue county, Min- 
nesota. The best exposure of these beds is in a bluff about thirteen miles south of Cannon Falls. 
