MADREPORARIA APOROSA. 



269 



teries correspond with especially deep intermesenteric pouches, 

 which fit into deep pits in the floor of the visceral chamber. These 

 pits are bounded by septa of much reduced size, and may be fairly 

 compared with the " fossula " of the Rugosa. 



This family comprises only the two genera Pocillopora and Seria- 

 topora, both of which, as above shown, have certain very remarkable 

 characters, and make a decided approach to the Rugose Corals. In 

 Pocillopora (fig. 145), there is a small columella, and well-developed 



b Ws 







• 



Fig. 145. — a. Portion of the corallum of Pocillopora aspera, var. lata, Verrill, of the natural 

 size ; b, Part of the surface of same, enlarged ; c, Section of the corallites of the same, showing 

 the columella, enlarged ; d, Vertical section of the same, enlarged, showing tabulae. (After 

 Dana.) 



tabulae (fig. 145, d) are present. The genus ranges from the Mio- 

 cene Tertiary. In Seriatopora, on the other hand, there is a large 

 compact columella, and only traces of tabulae are present. No fossil 

 forms of this genus have been hitherto discovered. 



Family 4. Astrceidce. — In this large family of the Aporosa the 

 corallum may be simple or composite. Endothecal tissue in the 

 form of dissepiments is well developed, and tabulae are present 

 in some forms. The septa are lamellar, their free edges being 

 sometimes smooth or entire, sometimes dentated or ragged. The 

 increase of the composite coralla (fig. 146) is effected by gemmation 

 or by fission, and the new corallites usually become united directly 

 by their walls or costae, or in other cases by vesicular exothecal 

 tissue, a solid ccenenchyma being rarely developed. 



If Columnaria be admitted into the Astrceidce, the family is 

 represented as early as the Ordovician period. The Silurian 

 genera Stauria and Acervularia (as typified by A. ananas), the 

 Devonian Battersbyia, and the Carboniferous Heterophyllia may 

 likewise be regarded as Palaeozoic types of the Astrceidce, though 

 all depart in different respects from the ordinary forms of this family. 

 Leaving the Palaeozoic period, we find a great development of 

 Astrceidce to take place towards the close of the Trias, where the 



