408 PROF. EHRENBERG ON FOSSIL INFUSORIA. 
von Humboldt, who lately visited the district of Bilin in his journey to 
Teplitz, and sent me two very rich collections of the mineral pro- 
ducts of that district, in various states, have furnished new materials 
for the furtherance of my observations. 
Before I speak of this valuable addition to our subjects for investiga- 
tion, I may mention, that an examination of the Polirschiefer of Planitz 
(of which, by the friendly intervention of M. Weiss and the liberality of 
M. Freiesleben in Freiberg, I have been enabled to examine a specimen 
whose locality was quite certain,) has shown with certainty that this 
layer also is a conglomeration of infusoria shells. The specimen exa- 
mined resembled the Saugschiefer of Bilin, and the infusoria shells of 
the Gaillonella distans are here filled with and connected by a siliceous 
cement, which somewhat mars the distinctness of their form; I have, 
however, seen some so plainly that I am convinced of the identity of 
these two formations. There is probably also in Planitz a more earthy 
form of this stone, similar to the loose. Polirschiefer, which is chiefly 
formed of the unchanged Gaillonella distans. 
A specimen of the Polirschiefer from Cassel, which M. Carus of Dres- 
den had the kindness to send me, and in which he had also recognized 
organic forms, was particularly interesting. 
I found in the Royal Mineralogical Cabinet some specimens with pe- 
trifactions of fish, the Leuciseus papyraceus, from the same locality. 
I have also lately been able, through the kindness of M. Keferstein of 
Halle, to examine specimens of the stone from the Habichtswald near 
Cassel. This Polirschiefer of Cassel contains seven different species of 
shield-infusoria, between which is a loose and, for the most part, siliceous 
cement, which cannot be plainly reduced to organic fragments. It is 
worthy of notice that most of the forms in the Polirschiefer from Bilin 
and Planitz are either extinct or as yet undiscovered ; while at the same 
time those forms which resemble existing species, belong to such as are 
not very striking, and therefore less sure for the detection of their iden- 
tity ; but in the Polirschiefer of Cassel two of the most remarkable exist- 
ing forms occur, namely Gaillonella varians and Navicula viridis: Na- 
vicula striatula appears also to occur in this Polirschiefer. Gaillonella 
varians and Navicula viridis appear both in the tertiary formation of 
Cassel and in the Bergmehl of San Fiore, and these have a form related 
to that of Navicula Follis. Besides 1. Gaillonella varians, 2. Navicula 
viridis, 3. Navicula striatula? 4. Navicula Crux (comp. Navicula 
Follis adulta), I have also found in the stone from Cassel, 5. Navicula, 
fulva juv.? 6. Navicula gracilis? and 7. Navicula Cari, n. species,— 
three less clearly defined species: the last however is very numerous 
and is unknown to me. Besides these ascertained relations of the distri- 
bution of the Infusoria-schiefer as Polirschiefer, the rich parcel sent by 
M. von Humboldt from Bilin and the valley of Luschitz has given rise 
