FOREIGN CORRESPONDENCE. 
149 
calix alone was known, being placed by me and by Mr. Phillips in 
Poteriocrinus, whereas in reality they belong to another genus, but of 
which it was impossible then to suspect the existence. 
These are Poteriocrinus granulatus, Phil., P. Calyx, M'Coy., P. 
Phillipsianus, De Kon., and P. Maccoyanus, De Kon. These species are 
distinguished, nevertheless, from the true Poteriocrini by the brevity 
and open form of their calix, which is usually conoid in the others. 
These latter appear to have smooth stems, formed of articulations, having 
very nearly the same diameter ; and, in consequence, not possessing 
the ringed character above referred to. Two of the species which I 
have to notice have been placed by Mr. M'Coy (Palseoz. Fossils in Mus. 
of Cambridge, p. 117), in the genus Cupressocrinus of Goldfuss; and I 
shall not now dwell on the inexplicable error committed by that palaeon- 
tologist, because I have already had occasion to refer to it in my 
" Eecherches sur les Crinoides" (p. 88). 
It is almost superfluous to add that the genus in question ought to 
be placed in the family of Poteriocrinidae. 
Distribution. — All the known species of Hydreionocrinus belong eX' 
clusively to the " Productus-bed" (P. giganteus.) of the carboniferous 
limestone. Most of the specimens have been found in England or in 
Scotland — some in the United States. The Limestone of Vise has 
furnished me with two, but one only is special to it. 
{To he continued.) 
FOREIGN COEEESPONDENCE. 
Bt De. T. L. Phipson, of Paeis. 
Mercury in the soil of Montpellier — Mud-volcanos of Javar^A.ncient 
siijierstitions — Fearful eruptions — Origin of the mud in these volcanos 
— Rarity of Sulphate of Potash in nature — Abundance of Sulphate of 
Soda — Beds of this salt in Spain. 
As early as the year 1 760, M. I'Abbe Sauvages made known to the 
■world that mercury, in a metallic state, existed in the soil on which 
the town of Montpellier is built — a discovery made by himself. Since 
that time Amoreux, Gouan, Gensanne, and Poitevin have successively 
mentioned the same fact. Poitevin, in 1830, remarked: "We must 
