SUESS—SHELL OF CEPHALOPODS. 11 
by an alternation of hydraulic marls and bituminous dolomites and 
limestones, characterized by the presence of a new species of Tra- 
chyceras, Tr. Attila, Mojs. The reddish-grey limestones of the 
upper horizon are equivalent to the ‘‘ Potschen” Limestones of the 
North and to the “ Buchenstcin” Limestones of the South Alps. 
The most frequent fossil forms in them are Ammonites (Arcestes) 
tridentinus, Mojs., sp. n., Am. Arpadis, Mojs. sp. n., and Halobia 
Lommeli, Wissm. Trachyceras Attila is of rare occurrence, as also 
in the “‘ Potschen” Limestones. Am. (Arc.) tridentinus, the most fre- 
quent form in the Bakonyan Limestone, as also in the ‘‘ Potschen ” 
and ‘‘ Buchenstein” Limestones, was first made known as of very 
rare occurrence in the Oenian porphyritic Tuffs of the South 
Alps, characterized by the presence of Trachyceras doleriticum and 
T. Archelaus. The Bakonyan Limestones, with Am. (Arc.) triden- 
tinus, are locally overlain by green tuffs. A ravine close to the 
marble-quarry of Csennye proved an abundant locality for Ammo- 
nites characteristic of the Inferior “* Dogger,” such as Am. Murchi- 
sone, Sow., Am. fallax, Ben., Am. scissus, Ben., Am. cf. tatricus, 
Pusch, Am. cf. gonionotus. They are found mixed with Am. sile- 
siacus, Opp., and Am. serus, Opp., from the Lias of the neighbouring 
quarry, and with an abundance of Fimbriati of at least two different 
species. A well-preserved specimen of Am. superbus, B., has been 
obtained from Somhegy. A bed of Liassic Limestone includes an 
enormous quantity of Brachiopods, among which Terebratula Aspasia, 
Men., predominates, but very few Ammonites. 
On the Structure of the Sprrat SHELL of CerHaLopops. 
By Prof. E. Svzss. 
[Proc. Imp. Acad. Vienna, March 10, 1870.] 
Dr. Carpenter first stated that the shell of Nautilus Pompilius 
consists of two strata, an outer testaceous one (the “ostracum”), and 
an inner one, of the nature and aspect of mother-of-pearl. The 
same is the case with the shell of Argonauta and of the Ammonites, 
the mother-of-pearl stratum constituting the septa of the chambers. 
Arcestes, Goniatites, Phylloceras, and Clymenia have besides a rugose 
stratum, rather answering to an imperfect formation of mother-of- 
pearl than the black stratum of Nautilus. In the above-named 
genera, the periodical constrictions take place under the form of 
varices, and in the rest of the Ammonitide in the form of contractions 
of the shell. Taken as a whole, the more ancient forms possess 
generally one chamber, including the whole animal, and really in- 
habited by it, while many of the comparatively more recent forms 
adhered only by muscular prolongations of the hind portions of their 
body, the other chambers serving only as an hydrostatical apparatus 
by whose aid the animals moved with more ease through the sea. 
The shell of the female Argonauta, provided with rudimentary shell- 
muscles, represents a rudimentary Ammonite shell, an “ ostracum ” 
without stratum of mother-of-pearl. -Argonauta is a member of an 
