SUB-ORDER B 



TREPOSTOMATA 



273 



Homotrypa,\Jlrich (Fig. 451). Generally ramose, sometimes frondescent. Zooccial 

 tubes with very thin and finely crenulated walls, and remote diaphragms in the 



section, 



I IO. l-'.l. 

 Ulr. Trenton ; Minnesota. A, Surface. B, D, Tangential sections. C, Vertical 



axial region. Cystiphragms, isolated or in series, developed in peripheral region only. 

 Apertures polygonal or sub-circular. Mesopores usually few and in clusters. Acan- 

 thopores generally present. Ordovician. 



Prasopora, Nich. and Eth. (Fig. 452). Zoarium usually free in adult stage, with 

 wrinkled epitheca on lower surface. Zooecial tubes prismatic or cylindrical, thin- 



Fio. 4:.L'. 



Proton . L'lr. TnMitnn ; 



Kentucky. 4,Tian8vene,an<] /;, Ver- 

 tical section, /, (aftr Ulrich). 



Fio. 453. 



, Ulr. Black River Group ; Minnesota. A, Trans- 

 verse section. B, C, Vertical sections, Wi (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. 



Zoaria frondescent, ramose, or parasitic. Zocecia polygonal, with moderately thin walls. 

 Acanthopores present, sometimes of large size. Diaphragms numerous, horizontal. Cysti- 

 phragms wanting. Ordovician. 



Dekayella, Ulrich (Fig. 454). Ramose, branches'sometimes compressed. .Mesopores 

 more or less numerously distributed among the zooecia. 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 

 MI Killer set of acanthopores, and lesser number of mesopores and diaphragms. 



Heterotrypa, Xich. (Fig. 185). Zoarium always frondescent, and acanthopores of 

 small size only ; otherwise like Dekayella. Abundant in Cincinnati Group. 



VOL. I T 



