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Eschar a also has not been found fossil ; its species would 

 be discovered by their flat, lamelliform, thin expansions, 

 with cellules in quincuncial order disposed on both sides 

 by which they may be distinguished from the millepores 

 and retipores. 



Adeona might be placed in the same genus as eschara, 

 but for its peculiar stem, which is sub-articulated and 

 covered with a superficial crust, and its leaf-formed ex- 

 pansions, which are covered with cellules, 



Retepora has also thin and flat expansions composed of 

 branches sometimes free, but most frequently anastomosing 

 in web-work or in fillets. The cells are disposed only on 

 one side, which distinguishes it from the adeonas and 

 escharas. It is not incrusting, which distinguishes it from 

 the cellepores. 



A fossil species has been found in the environs of Angers, 

 in small pieces, by M. Menard, which is thus described : — 

 Ret. frustulata. In flat pieces, in lattice work, with pores on 

 one side. 



Alveolites,— A lapideous polypifer, either incrusting or 

 in a free mass composed of many concentric tables, involving 

 each other. The tables are formed of tubulous, alveolar, 

 prismatic, short, contiguous, and parallel cellules, connected 

 externally in a net-work. — Lam. 



The greater part of the substances belonging to this 

 genus, Lamarck observes, are yet only known in a fossil - 

 state ; and of these he particularizes the following ; 



1. Alveolites escharoides. — Subglobose, the surface webbed with 



rhomboidal cells ; the margin of the cells biporous. 

 Found fossil, in the environs of Dusseldorf. In the cabinet of 

 Chevalier de Lamarck. A subglobular irregular mass, as big 

 as a middling-sized apple, formed of numerous layers, rather 

 thin, enveloping each other. 



2. Alv. suborbicularis. — Hemispherical ; the surface perforated with 



oblique subimbricated cells. 



