BRYOZOA. 285 
Diplotrypa.] 
pores. Zocecial apertures rounded, mostly subcireular, regular, twelve or thirteen 
in3 mm. Closures preserved in one out of about forty specimens, slightly concave, 
apparently smooth and without a raised rim about the central perforation. Walls 
of moderate thickness, ridge-shaped. Mesopores numerous, rather small, but dis- 
tinctly visible under a good pocket lens. 
Internal characters: These are remarkable chiefly in vertical sections, tangential 
and transverse sections being very much like those of C. pulchella and C. ramosa. 
In vertical sections namely there seems to be a total absence of diaphragms, not 
only in the zocecial tubes but in the mesopores as well. Another peculiarity is the 
crenulated or wavy character of the walls in the axial region that has suggested 
the specific name. This crenulation is shown very distinctly when the tubes are 
exposed by vertical fractures. 
The two peculiarities mentioned in the preceding paragraph distinguish the 
species from all the others now referred to the genus. In other respects we are 
reminded of its associate C. pulchella, yet they ought in no case to be confounded, 
since in that species the branches are more slender and do not inosculate, and the 
zocecial apertures are appreciably smaller. 
Formation and locality—Not uncommon in the upper third of the Trenton shales at St. Paul and 
near Cannon Falls, Minnesota. Rare in the Galena shales (here almost invariably without monticules) 
at the same localities, and at Decorah, lowa, and Neenah, Wisconsin. 
Mus. Reg. Nos. 8019, 8038, 8068, 8082. 
Family DIPLOTRYPIDA, Ulrich. 
For remarks on this family see pp. 276 and 290. 
Genus DIPLOTRYPA, Nicholson. 
Zoaria massive or discoid, generally free. Zocecial tubes comparatively large, 
with thin prismatic walls, and horizontal diaphragms. Mesopores few to numerous, 
varying in size, many of them enlarging gradually and assuming the characters of 
true zocecia. Acanthopores wanting. 
Type: D. petropolitana Pander, sp. 
The relations of this genus are with Batostoma on the one hand and Monotrypa 
and Callopora on the other. Species are few and, so far as known, all belong to Lower 
Silurian rocks, The two about to be described are aberrant in having very few 
mesopores. 
