BRITISH ASSOCIATION MEETING. 
535 
modem geuera of VaionuJ^e are generally strongly toothed, except the thin 
Anodoii and its allies. Again, they have a thick wrinkled epidermis. 
Uiiionida have not this, Mi/ada have, and the ligament is internal, as iu 
many Mycida;. The shape is oval, broadest in front, beneath the beaks. 
Anthracomya. — Generally found with AiUhracosia ; differs materially ; the 
shape is broadest posteriorly ; the shell thinner ; hingeless (so far as known) ; 
epidermis wrinkled. 
Myalina ? — Quadrate shells, slightly iiiequivalve, but not at all so much so 
as Acicu/a, and with no produced hinge-line, and no teeth. Mi/aUna 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 could substantiate the marine character of any one, wc 
should be sure of the rest. And this is the point to Mhich the attention of 
couchologists should be directed. It is not yet certain that the Anthi-acomya 
is really allied to the Mya, though its want of hinge and wrinkled thick epi- 
dermis favours the view. Nor do these shells, or Anthraeos'ui, except very 
rarely, occur with undoubted marine shells, Pfoduday Sj)iri/ej'y or Cephalopodous 
mollusca. 
But then, against the idea of their being freshwater forms, there is the fact 
that no shells like Paludim or Mela/iia, 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 scam 
and locality, and endeavour to ascertain what species are peculiar to each bed. 
The plants are likelj to be more generally spread, and, indeed, wc already 
know more about theu' distribution. 
ON AN ALUMINOUS MINERAL 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 wliich about half the silicic acid was re- 
placed by carbonic acid. 
