ORDP]R III 



TREPOSTOMATA 



333 



separated froni one aiiother by smaller angiüar mesopores, and contaiiiing cystiphgrams. 

 Acantliopores usiially pre- 

 sent. Ordovician and 

 Silurian. 



Mesotnjpa Ulr. (Fig. 

 479). Äspidopora Ulricli. 

 Ordovician and Silurian. 



Family 2. Heterotry- 

 pidae Ulrich. 



Zoaria frondescent, 

 ramose, massive or jjara- 

 sitic. Zocecia polygonal, 

 lüith moderately thin lualls. 

 Äcanthoporespresent, some- 

 times of large size. Diaphragma numerous, horizontal. Cystiphragms ivanting. Ordo- 

 vician to Devonian. 



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



Fig. 479. 



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

 section. B, C, Vertical sections, i4/j (after Ulrich). 



! I T / > '■ ■'' 



!/ 1/ / ,■'/ 



Fig. 480. 



Dehiyella ohscura (Ulr.). Ordovician ; Cincinnati, Ohio. 

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



Fig. 481. 



Dekayia aspera Edw. 

 and H. Ordovician ; Cin- 

 cinnati, Ohio. Tangential 

 section, ^■^/i. 



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

 only in the peripheral region. Ordovician and Silurian. 



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

 Ordovician and Silurian. 



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



Fig. 482. 



Stigmatella foordi (Nich.). Ordovician ; Es- 

 thonia. A, Tangential section, i^i. B, Vertical 

 section, 22/j (after Bassler). 



K^'i'Kj'^'pi'^^ 



•^/?iS^lÄÄ 



Fig. 4S3. 



Ätactopora maculata Ulr. Ordovician ; Cincinnati, 

 Ohio. Transverse and vertical sections, n/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, ^, ^). Ordovician and 

 Silurian. 



