ORDKR III 



TREPOSTOMATA 



333 



sej)fii'<ited from one anotlier by smaller angular mesopores, and containing cystiphgrams. 

 Acantliojiores visually pre- 

 sent. Ordovician and 

 Silurian. 



Mesotrypa Ulr. (Fig. 

 479). Asindofora Ulrich. 

 Ordovician and Silurian. 



Family 2. Heterotry- 

 pidae Ulrich. 



Zoaria frondescerd, 

 ramose, massive or i^ara- 

 sitic. Zocecia polygonal, 

 v'ith moderately thin icalls. 

 Acantlioporesf resent, some- 

 times of large size. Diaphragms numerous, horizontal. Cystiphragms tcanting. Ordo- 

 vician to Devonian. 



Dekayella Ulr. (Fig. 480). Zoarium always frondescent, mesopores numerous, 



> '' / '■' A'^'-* 



Fig. 479. 



Mesotrypa infida Ulr. Black River Group ; Minnesota. A, Transverse 

 section. B, C, Vertical sections, n/i (after Ulricli). 







Fk;. 480. 



Dekayella dbscura (Ulr.). Ordovician ; Cincinnati, Ohio. 

 Tangential and vertical sections, n/i (after Ulrich). 



Fi<;. 481. 



Di'Xayia aspera Edw. 

 and H. Ordovician ; Cin- 

 cinnati, Ohio. Tangential 

 section, i4/j. 



and acantliopores of two sizes, the smaller ones the more abundant, and present 

 only in the peripheral region. Ordovician and Silurian. 



Heterotrypa Nich. Zoarium frondescent, and acanthopores all of uniform size. 

 Ordovician and Silurian. 



Dekayia E. and H. (Fig. 481). Distinguished from Heterotrypa by the absence of 

 A B 



Fig. 48-2. 



Stigmatella foordi (Nich.). Ordovician ; Es- 

 thonia. A, Tangential section, w/i. B, Vertical 

 section, 22/j (after Bassler). 





Fig. 483. 



Atactoponi maculata Uli. Ordovician; Cincinnati, 

 Ohio. Transverse and vertical sections, i-i/i, showing 

 greater part of a solid macula (after Ulrich). 



the smaller set of acanthopores, and lesser number of mesopores and diaphragms. 

 Ordovician. 



Petigopora Ulrich. Stigmatella Ulr. and B. (Fig. 482, A, B). Ordovician and 

 Silurian. 



