MODERN CLASSIFICATION. 
239 
which is seen on the mould of the body- chamber, but is seldom visible on the chambered 
portion of the shell. Horny Aptychus probably present in Arcestes, certainly in Amal- 
them, for the other forms doubtful. 
Gems Arcestes, Suess. — Shell in general smooth, seldom with longitudinal lines ; 
body-chamber long, from one to one and a half whorls. Spiral increase moderate ; strongly 
involute ; mouth-opening contracted, either by an eversion of the shell, or through a 
thickening of its inner lamina around the border. Lobes strongly incised, so that the 
saddles consist of a small stem, with numerous approximated horizontal branches, from 
which other bifurcations proceed. The umbilicus is often closed by shelly eversion. 
Dr. Ed. V. Mojsisovics divides the genus into the following groups : — Extra-labiati, 
Sub-labiati, Bi-carinati, Coloni, Intus-labiati, Galeati, and Sub-umbilicati, all of them 
characterised by more or less modified body-chambers of the full-grown individuals, and 
by a contraction of the umbilicus, frequently entirely occluded by a callosity. All these 
forms are accurately figured from perfect specimens in his splendid Monograph.-^ 
The typical Arcestes belong to the Trias. The species number about 130, and the 
Muschelkalk contains some highly developed forms. I cite three well-known species 
as types of this genus : Arcestes suh-umbilicatus, Bronn, Arcestes Gaytani, Klipstein, 
Arcestes Johannis-AustricB, Klipstein. 
Gems'Dimm.ii:^^, v. Mojs. — General form and length of chamber as in the preceding; 
shell provided with folds and well-defined lines of growth ; through the whole length of 
the body-chamber up to the mouth-border there rises npon the convexity of the 
inner side of the shell a median ridge (normal line). The whorl is contracted near the 
mouth. The lobe-line is formed by a few pairs of small incised saddles which frequently 
alternate with single saddles. The radial lines of growth on the shell, the median 
ridge on the ventral surface, and the pecuhar arrangement of the lobe-line distinguish 
Bidymites from Arcestes. All are collected from the Noric stage or division (Norische 
Stufe) of the Trias, near Hallstatt. 
Genus Lobites, v. Mojs. — In the general form and length of the body-chamber it 
agrees with Arcestes and Bidymites. Shell with transverse folds 
which are abundantly intersected with fine longitudinal lines. The 
last whorl takes on frequently a shape different from the form of the 
internal cast, and not unfrequently closes the umbilicus with a 
callosity. Most of the species are found in the Triassic beds 
(Carinthian division) with Lobites ellipticiis at Rothelsteins. I have 
cited as a typical example (fig. 133) Lobites delphinocephalus, Hauer, ^ ^ ^.^ 
from that locality. deipMnocephaius. 
^ ' Das Gebirge um Hallstatt,' 4to., with 70 plates, Wien, 1875. 
