SUB-ORDER B TREPOSTOMATA on 
Homotrypa, Ulrich (Fig. 451). Generally ramose, sometimes frondescent. Zoccial 
tubes with very thin and finely crenulated walls, and remote diaphragms in the 

Fie. 451. 
Homotrypa subramosa, Ulr. Trenton; Minnesota. A, Surface. B, D, Tangential sections. C, Vertical 
section, 14/). 
Cystiphragms, isolated or in series, developed in peripheral region only. 
axial region. 
Mesopores usually few and in clusters. Acan- 
Apertures polygonal or sub-circular. 
thopores generally present. Ordovician. 
Prasopora, Nich. and Eth, (Fig. 452). Zoarium usually free in adult stage, with 
wrinkled epitheca on lower surface. Zocecial tubes prismatic or cylindrical, thin- 
B C 





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Fia. 452. . 
Prasopora simulatriz, Ulr. Trenton; Hue eas 
Kentucky. 4A, Transverse, and B, Ver- Mesotrypa infida, Ulr. Black River Group; Minnesota. A, Trans- 
verse section. B, C, Vertical sections, 14/; (after Ulrich). 
tical section, 14/; (after Ulrich). 
walled, separated from one another by smaller angular mesopores, and containing 
cystiphragms. Acanthopores usually present. Ordovician. 
Mesotrypa, Ulrich ; Ordovician. Aspidopora, Ulrich ; Ordovician and Silurian. 
Family 2. Heterotrypidae. Ulrich. 5 
Zoecia polygonal, with moderately thin walls. 
Zoaria frondescent, ramose, or parasitic. 
Diaphragms numerous, horizontal.  Cysti- 
Acanthopores present, sometimes of large size. 
phragms wanting. Ordovician. 
Dekayella, Ulrich (Fig. 454). Ramose, branches sometimes compressed. Mesopores 
more or less numerously distributed among the zoccia. Acanthopores of two sizes, 
the smaller ones the more abundant, and present only in the peripheral region. 
Dekayia, Ed. and H. (Fig. 455). Distinguished from Dekayella by the absence of the 
smaller set of acanthopores, and lesser number of mesopores and diaphragms. 
Heterotrypa, Nich. (Fig. 185), Zoarium always frondescent, and acanthopores of 
small size only ; otherwise like Dekayella. Abundant in Cincinnati Group. 
VOI. Jt; 
