Unger on Fossil Plants —T’schermak on Feldspars. 445 
M. Suess has recognized on these specimens, the head with the man- 
dible, the arms furnished throughout their length with a double row of 
hooks, the ink-bag, the dorsal shield and phragmacone, with the cham- 
bers, the ligatures, traces of the siphuncle, and here and there some 
remains of the mantle. The dorsal shield, hitherto unknown as to 
its form, presents two concave lobes behind the hyperbolar region. 
The alveolus, distinguished by the abnormal strie of growth lately 
noticed by Prof. Huxley as probably belonging to a new type of 
Belemnites, is considered by Prof. Suess to, belong to the genus 
Acanthoteuthis.*—L’ Institut, 5th July, 1865.—J. M. 
II. Pror. UNGER on THE Fossit PLANnts oF HuNGARY. 
‘PROF. UNGER has presented to the Academy of Sciences of 
Vienna a Memoir on the Fossil Plants of Hungary and Transyl- 
vania, in which he treats specially of those found by M. Stur in the 
Upper Cretaceous Deposits of Déva, Transylvania. All the specimens 
are well preserved, so that they can be recognized with certainty 
as belonging to genera allied to those of the present day; a fact of 
much importance in the determination of the Dicotyledonous plants 
of the Cretaceous period.—L’ Institut, 12th July, 1865.—J. M. 
III. On tHe Group or Feipspars. By M. Tscuermax. 
| eS minerals, abundantly distributed in certain rocks of the 
globe, are interesting to the chemist, mineralogist, and geo- 
logist, and have been the subject of numerous memoirs. The 
continued chemical researches on these mirerals have increased 
their complication—substances identical by their physical characters 
being often found chemically very different ; some not assuming a 
‘definite character, others inconsistent with a systematic classifica- 
tion—more especially the feldspars, containing both soda and lime. 
According to the opinion more than once advanced, the feldspars 
could only be mixtures of isomorphous combinations. M. Tscher- 
mak considers that in reality all the feldspars are only mixtures of 
three substances, which exist in nearly a pure state in adularia, 
albite, and anorthite. 
The potash-feldspars, comprised generally under the name of 
orthoclase, are regular mechanical combinations of orthoclase and 
albite, which, however, are not isomorphous, orthoclase crystallizing 
in the monoclinic and albite in the triclinic system. The constant 
combination of particles of albite gives rise to forms of dimensions - 
similar to those of adularia; and thus the accession of the albite, 
although not isomorphous in itself, only modifies very slightly the 
form of orthoclase. 
All the other feldspars are isomorphous mixtures of albite and 
anorthite, to which, in certain cases, orthoclase is added in small 
quantities. 
* See Guor, Mac., Feb. 1865, p. 67. 
