BRITISH ASSOCIATION MEETING, 



535 



modern genera of Unionidce are generally strongly toothed, except the thin 

 Anodon and its allies. Again, they have a thick wrinkled epidermis. 

 Unionidce have not this, Myadce have, and the ligament is internal, as in 

 many Myadce. The shape is oval, broadest in front, beneath the beaks. 



Anthracomya. — Generally found with Anthracosia ; differs materially; the 

 shape is broadest posteriorly ; the shell thinner ; hingeless (so far as known) ; 

 epidermis wrinkled. 



Myalina ? — Quadrate shells, slightly inequivalve, but not at all so much so 

 as Avicula, and with no produced hinge-line, and no teeth. Myalina has an 

 area. Their place is doubtful, and all their analogies are with marine genera. 

 Epidermis not yet observed as wrinkled. These three genera constantly occur 

 in society. 



If, therefore, we conld substantiate the marine character of any one, we 

 should be sure of the rest. And this is the point to which the attention of 

 conchologists should be directed. It is not yet certain that the Anthracomya 

 is really allied to the Mya, though its want of hinge and wrinkled thick epi- 

 dermis favours the view. Nor do these shells, or Anthracosia, except very 

 rarely, occur with undoubted marine shells, Prod?icta, Spirifer, or Cephalopodous 

 mollusca. 



But then, against the idea of their being freshwater forms, there is the fact 

 that no shells like Paludina or Melania, or any of the familiar forms in the 

 Purbeck or Wealden deposits, occur in the coal bands. The bivalves were 

 certainly not purely freshwater. They were probably not even inhabitants of 

 the open sea. They lived most likely in muddy lagoons of quiet salt-water, 

 and hence the peculiar and marked character of these characteristic coal-shells. 



It is desirable that all who may have opportunity/by means of their workmen, 

 of collecting carefully, should obtain these shells in quantity from each seam 

 and locality, and endeavour to ascertain what species are peculiar to eacli bed. 

 The plants are likely to be more generally spread, and, indeed, we already 

 know more about their distribution. 



ON AN ALUMINOUS MINEEAL FROM THE UPPER CHALK, NEAR 



BRIGHTON. 



By Messrs. J. H. and G. Gladstone. 



The author said that in an old chalk-pit, at Hove, there are many faults, and 

 some of them are filled up with a white mineral that runs along the dislocated 

 layers of flint, and sometimes embeds the shivered fragments. It has the 

 form of agglomerated masses, which are porous, and easily fall to pieces. One 

 piece that was analysed proved to be well defined hydrated bisilicate of alumina 

 — that which has received the name of collyrite — with no other impurity than 

 one per cent, of carbonate of lime. Its specific gravity is 1.99. Another 

 piece contained thirteen per cent, of carbonate of lime, and five per cent, of 

 additional carbonic acid, which must have been combined with the alumina. 

 As the silicic acid was proportionately smaller in quantity, this piece of the 

 mineral was viewed as collyrite in which about half the silicic acid was re- 

 placed by carbonic acid. 



