FAMILIES AND GEISTERA OF THE MADBEPORABIA. 123 



XI. Alliance ISASTR^OIDA. 



Agglomerate Astraeidse, increasing by gemmation within the calice 

 Walls of corallites fused. Occasionally the fusion is deficient near the 

 calice or low down. Septa denticulate or entire. 



Tribe I. Septa denticulate. 



Genus IsASTRiEA, Ed. & H. 

 Genus Prionastr^a, Ed. & H. 

 Genus Placastr^a, Stol. 

 Genus Elysastr^a, Laube. 

 Genus Lepidophylua, Duncan. 



Tribe II. With entire septa. 



Genus Aploccenia, Ed. & H. 

 Genus absorbed : — 



Metastr^a, Ed. & H. 



Tribe I. 



Genus Isastb^a, Milne-JEdwards Sf Jules Saime, Hist. Wat. des 

 Gorall. vol. ii. p. 526 (1857). 



Colony massive, convex, gibbous, subdendroid or incrusting. 

 Corallites prismatic, and intimately united by tlieir walls, whicb 

 are simple throughout. The calices have a polygonal outline, 

 which is simple and ridge-like. The columella is rudimentary 

 or absent. The septa are thin, close, granular, denticulate. 

 Eudotheca fairly well developed. The common base is marked 

 with fascicles of costse, and has a thin epitheca. G-emmation 

 calicinal and submarginal. Occasionally the calicular walls are 

 slightly apart near the calice. 



Distrihition. — Fossil. Trias: Europe. Infra-Lias, Lias, Oolites: 

 England and Europe. Cretaceous : England, Europe, India. 

 Eocene : Europe, India (Sind). Miocene : West-India Islands. 



Genus Peiokastr-SIA, Milne-Fdwards Sf Jules Saime, Hist. 

 Nat. des Oorall. vol. ii. p. 513, pi. D 8. fig 1 (1857). . 



Syn. Metastrcea, Ed. & H. 



Colony large, massive, convex, with or without ascending lobes, 

 subplane, hemispherical, gibbous. Corallites close, prismatic ; 

 their walls are united above but usually not below. Calices 

 polygonal and deep, or not large ; margins simple or in crests. 

 Columella spongy, variable in development. Septa thin, narrow 

 above, close, granular, and very finely serrate, the longest teeth 



