Litliothamnium. It occurs abundantly in Hungary and 
Switzerland. The so-called pisolithic limestone of Paris is 
according to Giimbel about eight tenths stone algse ; also 
M. Mario, Astrup; the pleiocene of Castel Arquato; and in 
fact it seems to be found in most of the tertiaries on the 
continent. It is further found in the chalk at Maestricht, 
and in the Jurassic sponge beds at Schwabenbergs. 
Doubtless when geologists have paid more attention to 
the question we shall find it has a very wide distribution, 
and has formed rocks of equal importance in other parts of 
the world. 
Taking the Eastern Alps, witli which I have a fair 
acquaintance, viz., the Bavarian, Austrian, and North Italian 
Alps, in whicli, as you know, the tertiary deposits attain 
extraordinary importance, I do not think it is too much to 
say that one sixth of the whole tertiary rocks of this district 
are composed of Lithothamnium. This is not given in any 
way as an exact calculation, but merely to give an idea of 
its importance. 
The recent Melobesiacea seem to have a very general dis- 
tribution. They grow at but moderate depths. 
The Lithothamnium belongs to the family Melobesiacea 
of the order Floridese or Ehodospermefe ; a large number of 
this order are limesecreting, but these (Lith.) difier very 
materially from the Corallina, since in the former the car= 
bonate of lime is deposited in and between the cell structure, 
while with the Corallina the plant is filiform, and the lime 
is deposited round this, entirely encrusting it, It seems the 
structural difterence is sufficient to separate them into two 
entirely distinct classes. 
Giimbel, after saying how the stems and branches of a 
species are subject to variation as wed as the superficial 
characteristics, says, But by far the most important and 
numerous species can scarcely be distinguished by any other 
method than by the form and relative size of the cells. 
