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 zocecial 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 zocecial walls in the larger 

 species never get to be as thick as has been observed in sections of II. exilis. 



Formation and locality. Not uncommon in the lower third of the Trenton shales at Minneapolis, 

 Minnesota. 



Mus. Reg. Nos. 5976, 7655. 



HOMOTRYPA SEPARATA, H. Sp. 

 PLATE XIX, FIGS. 17-20. 



In its growth a-nd, 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 //. separata has an abundance of mesopore-like depressions 

 at the angles of junction between the zorecia, with aggregations of such depressions 

 in the maculae (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, place 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, Chatfleld, and near 

 Preston. Minnesota. 



Mus. Reg. Nos. 7667, 8122. 





