70 



Fossil, from the environs of Dusseldorf, in the cabinet of Chevalier 

 de Lamarck. 



These are in masses rather large ; they are convex, and almost 

 tm'binated on one side ; flattened and even a little concave on 

 the other ; being of irregular hemispherical shapes. The beds 

 are of a moderate thickness, the inner ones being the thinnest ; 

 the tubes which by their union form these layers are very much 

 inclined. 



3. Alv. madreporea. — Oblong, smooth, subramose, and reticulated 



on the hollow surface. — Guettard. Mem. Tom. iii. PL 56, fig. 2. 



Fossil, from the environs of Dax, in the cabinet of Chevalier de 

 Lamarck. 



This alveolite has the appearance of a long, rolled fossil madrepore, 

 with cells, not projecting as in the madrepora porites ; but the 

 examination of its interior part discovers a considerable dif- 

 ference, and shows that the mass is a compound of pentagonal 

 and hexagonal tubular cellules, placed in layers on each other. 



4. Alv. incrustans. — Incrusting marine bodies, the outer surface 



reticulated ; the cells prismatic, vertical, unequal, and close 

 together. 

 Its crust is composed of a single layer of closely set tubes ; the 

 surface presents outwardly a net-work of small, unequal, pen- 

 tagonal, or hexagonal meshes. 



These fossils are perhaps not very frequent in this 

 island : I know but of two ; one of which appears to belong 

 to the last species, Alv. incrustans. The polygonal septa 

 dividing the meshes exist in the cavities and pass into the 

 substance of a gravel flint, with the localities of which I am 

 uninformed. A portion is shown, PI. x. fig. 11. 



The other is of an hemispherical form, and is, com- 

 paratively, a very large mass, being more than fifteen inches 

 in diameter. It is composed of concentric tables, about half 

 an inch in thickness, involving each other, and formed of 

 alveolar, prismatic, parallel and contiguous cells. It was 

 found in a mass of Portland stone ; and by exposure to the 

 weather has undergone such separations of its external 



