MADREPORARIA PERFORATA. 



315 



corallum is usually lobate or dendroid, and the corallites have their 

 walls more or less extensively thickened by a secondary deposit of 

 stereoplasma, the visceral chambers thus becoming more or less 

 contracted, especially in the peripheral region of the colony (fig. 197). 



Fig. 196. — Fragment of Favosites {Em- Fig. 197. — a, Transverse section of a few coral - 

 vionsia) hemispherica, of the natural size, lites of Pachypora Xichoho7ii, Freeh, from the De- 

 Devonian, America. (After Billings.) vonian of the Eifel, enlarged seven times, showing 



the thickened walls of the corallites ; b, Vertical 

 section of a few tubes of the same, p, Mural pores. 

 (Original.) 



The tabulae in this genus are straight and complete ; the septa are 

 usually rudimentary ; and the mural pores are generally large and uni- 

 serial, being converted into tubes in the more highly thickened por- 

 tions of the corallites. The species of Pachypora are mostly Silurian 

 and Devonian, but some forms appear to occur in the Carboniferous 

 rocks. Closely related to Pachy- 

 pora is the Silurian and Devonian 

 genus Striatopora (fig. 198), in 

 which the corallites also have 

 greatly thickened walls, but the 

 calices are surrounded by a cup- 

 shaped thickened margin, the 

 floor of which is striated by 



rudimentary Septal ridges. An- Fig. 198.— Fragment of Str/atoporajtexuosa 



, ,.. , . ■ /? of the natural size, and two calices enlarged. 



other allied type is the genus Silurian. (After Hail.) 



Trachypora, the species of which 



are principally Devonian. Here we may also place the curious 



Silurian genus Laceripora, in which the mural pores are uniserial 



and of large size, and the septa are in the form of marginal ridges. 



The genus Alveolites is the type of another group of Favositidcz 

 in which the corallites are usually more or less compressed, so as 

 to appear triangular, or semilunar, or crescentic when transversely 

 divided. The septa are usually present in the form of one, two, 



