XArTILlDJE. 
1S9 
Sj). CJuir. Shell compressed on the sides and narrowly truncated 
on the periphery, the whorls thus presenting a triangular section, 
the base of the triangle being the dorsal (inner) side of the shell. 
The periphery is shallowly concave and bounded by two prominent 
ridges. The greatest width of the whorls is in the region of the 
umbilicus. The latter is very small. The septa are approximate ; 
the sutures form two prominent lobes directed towards the aperture 
and separated by a deep and narrow sinus. The broader of the 
lobes is situated in the region of the umbilicus, the narrower one 
near the peripheral margin. A shallow sinus is formed by the 
sutures in crossing the periphery. The siphuncle is not known. 
The test is ornamented with thick and somewhat obscure and distant 
transverse, falciform folds, which form a sort of elbow at about the 
middle of the sides of the shell, their convexity being directed for- 
wards, not backwards as in some species of Ammonites having 
similar ornaments (e. g. Harpoceras falciferiim). 
liemarJcs. A fine example of this species is figured by Mojsisovics \ 
in which the test is very well preserved. The species which is 
nearest to the present one is KautiJus {Chjdonautilus) Salisbur- 
fjensis, v. Hauer ^ ; but the latter is a flatter shell with a much 
narrower periphery, the sutures also are more sharply bent than 
they are in J^aut. (Clydonaittilus) Quenstedti. 
Horizon. Tipper Muschelkalk. 
Locality. Hallstadt. 
llepresented in the Collection by a fragment (No. 22485). 
JUEASSIC SPECIES. 
Nautilus striatus, J. Sowerby. 
1817. Nautilus striatus, J. Sowerby, Min. Couch, vol. ii. p. 183, pi. 
clxxxii. 
1820. Nautilus aratus, Schlotheim, Die Petrefactenkunde, p. 82. 
1829. Nautilus striatiis, De la Beche, Trans. Geol. Soc. ser. ii. vol. ii. 
p. 27. 
1830. Nautilus yiganteus (Schiibler), Zieteu, Les Petrifications de 
Wurtemberg, livr. i. p. 23, tab. xvii. if. 1 «-c, & f. 2. 
? 1836. Nautilus aratus, Roemer, Die Versteiner ungen des Norddeuts- 
chen Oolithen-Gebirges, p. 178. 
^ Das Gebirge um Hallstatt (Abhandl. der k.-k. geol. Reichsanst.), Band vi. 
1873, p. 22, Taf. ix. ff. 1 a, 1 h. 
^ Neue Ceph. v. Hallstatt uucl Aussee, in Haidinger's Aatunviss. Abhandl. iii. 
p. 7, Taf. ii. ff. 4-8. 
