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 Trachyceras,
Tr. Attila, Mojs. The reddish-grey limestones of the
upper horizon are equivalent to the " Potschen " Limestones of the
North and to the " Buchenstein " 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 frequent
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.) tridentinus,
are locally overlain by green tuffs. A ravine close to the
marble-quarry of Csennye proved an abundant locality for Ammonites characteristic of the Inferior " Dogger," such as Am. Murchisonoe,
Sow., Am. fallax, Ben., Am. scissus, Ben., Am. cf. tatricus,
Pusch, Am. cf. gonionotus. They are found mixed with Am. silesiacus,
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 Spiral Shell of Cephalopods. By Prof. E. Suess.
[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 Ammonitidoe 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 inhabited 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
