238 THE PALEONTOLOGY OF MINNESOTA. 
(Homotrypa (?) intercalaris. 
HomorryPa (?) INTERCALARIS, 7. SD. 
d 
be = 
See Sees 
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Fia. 13. Homotrypa (?) intercalaris, n. sp., middle Trenton shales, Minneapolis, Minnesota. Collec- 
tion of EB. O. Ulrich. a and 6b, a specimen of the natural size, and small portion of its surface x18, showing 
unusually oblique zocecial apertures; ¢ and d, similar views of a fragment of a form doubtfully referred to 
this species, having somewhat smaller zocecia and mural papilla; e and f, similar views of a typical 
example; g, more slender fragment, natural size; h, tangential section, x18, showing structure immediately 
beneath surface of fully matured example; 7, another portion of same section, showing structure at a deeper 
level; j, vertical section, x18, showing the peripheral region with the mesopores and cystiphragms, and a 
smal! part of the untabulated axial region. 
Zoarium small, ramose, branches subcylindrical, generally 2.5 to 3.5 mm. in 
diameter. Surface without monticules but exhibiting distinct clusters of large cells 
in the centers of which there is often a small aggregation of mesopores. Zocecial 
apertures rounded or subangular, commonly direct to the surface, at other times 
more or less oblique, occasionally so much so (see fig. 13 6) that they recall those of 
Ceramoporella. The last condition probably occurred only when a new layer of zocecial 
tubes was developed in which the individual cells failed to correspond exactly with 
those of preceding layers. Typical form with about thirteen zocecia in 3 mm.; the 
variety, also figured above,.has fifteen in the same distance. Walls or interspaces 
of moderate thickness, commonly with very few and inconspicuous acanthopores. 
But in the variety a row of minute papille has been observed along the center of 
the wall. Mesopores rather abundant, occurring at most of the angles of junction 
between the zocecia. 
The internal structure is brought out sufficiently in the accompanying cut. 
Figures h and i show how very similar tangential sections may be to those of the 
7 
