BRYOZOA. 237 
Homotrypa separata.] 
especially in the clusters just mentioned. Diaphragms wanting in the axial region, 
but present in the short and rather abruptly bent peripheral region, in which the 
walls are also thickened and a series of cystiphragms developed. 
This clearly is not the young of H. minnesotensis. The specimens viewed under 
a hand lens show more direct and rounder zoccial apertures, with the mesopores 
also more abundant, and on the whole have a more matured appearance than many 
much larger specimens of that species. Furthermore, the zoecial walls in the larger 
species never get to be as thick as has been observed in sections of /7. exilis. 
Formation and locality.x—Not uncommon in the lower third of the Trenton shales at Minneapolis, 
Minnesota. 
Mus. Reg. Nos. 5976, 7655. 
HomMoTRYPA SEPARATA, 2. Sp. 
PLATE XIX, FIGS. 17-20. 
In its growth and, with the exception of one feature, also in its internal charac- 
ters, this species is very similar to H. minnesotensis, As it also occurs in the same 
beds with that species, a detailed description is unnecessary. A comparison of the 
two forms brings out that H. separata has an abundance of mesopore-like depressions 
at the angles of junction between the zocecia, with aggregations of such depressions 
in the maculi (see fig, 19), causing the zocecial apertures to be rounded—commonly 
subcircular instead of angular. Internally these interspaces give, to tangential sec- 
tions especially, a very different appearance from those of H. minnesotensis (compare 
figs. 3 and 4 with 17 and 18, plate XIX). Vertical sections of the two species are 
more alike, the only difference worthy of notice being the numerous presence 
of mesopores in the one and almost total absence in the other. Despite the obvious- 
ness and, in most other cases, the importance of a difference like that existing 
between these two forms, I cannot doubt that they are in reality closely related. 
Formation and locality.—Lower third of the Trenton shales at Minneapolis, Chatfield, and near 
Preston, Minnesota. 
Mus. Reg. Nos. 7667, 8122. 
