L. F. Spath—Ammonites from Spitsbergen. 299 
Mojsisovics,! namely Arctoceras polare (Mojs.), A. simplex (Mojs.), 
A. whitei (Mojs.), A. blomstrandi (Lindstrém), A. lindstroma 
(Mojs.) 2, A. dbergi (Mojs.), A.? costatum (Oberg). A number of 
small specimens, more evolute than the large examples, have 
lateral folds, or almost a spiniplicate ornament; but they occur 
with the young of undoubted Arctoceras, and, apparently, are 
connected with these by transitional forms. This may only be a 
case of convergence, for it is improbable that a spiniplicate develop- 
ment would give rise to forms that acquire costation on the outer 
whorl, as does Arctoceras. Only the smooth and more involute 
young, therefore, are considered to belong to Arctoceras. The others 
are like the young of “ Ceratites”’ decipiens Mojsisovics, and of 
Olenekites, e.g. O. sigmatoideus, Mojsisovics sp. The latter also 
resemble the young of forms referred to below as gen. nov. (Danubites?, 
Xenodiscus ?) and Mojsisovics® derives Danubites from Olenekites. 
The small forms, here compared with Olenekites, however, have a 
smooth ventral area, whereas in the gen. nov. there are constrictions 
across the venter, apparently arising from a spiniplicate ornament. 
It is impossible to say at present whether Arctoceras should be 
attached to Dinarites (in Mojsisovies), to Olenekites and Keyserlingites 
(in Hyatt), to Flemingites (in Philippi), or to Meekoceras (in Stolley). 
The writer may add that a true spiniplicate Olenekites in the 
British Museum is distinguished from the small forms here discussed 
by its square saddles, characteristic for Dinaritide. 
Four specimens consist of umbilical impressions of very large 
shells, probably A. lindstrimi, Mojsisovics sp. ; their matrix indicates 
the Posidonomya shales. Fifteen examples are merely impressions 
in more or less weathered slabs of rock. But, whereas the well- 
preserved specimens and the umbilical casts above referred to 
clearly come from the Posidonomya shales * and generally are 
associated with numerous examples of Posidonomya mimer Oberg, 
these impressions are preserved in a very fine-grained black lime- 
stone, weathering yellow, and including (besides ?- H@rnesia) large 
smooth Pseudomonotis of the type of P. (Claraia) decidens (Bittner)? 
1“ Arktische Triasfaunen’’: Mém. Acad. Imp. Sci. St. Pétersbourg, ser. VI, 
vol. xxx, No. 6, 1886, pp. 29-38. a 
2 Non “ Arctoceras’”’ lindstrémi. J. Bohm in J. G. Andersson (‘‘ Ub. d. 
Stratigr. und Tektonik d. Baren-Insel’’: Bull. Geol. Inst. Univ. Upsala, 
vol. iv, 1899, pt. ii, No. 8 (1900), p. 265), a Nathorstites, that has nothing to do 
with the Lower Triassic Arctoceras lindstrémz (Mojsisovics). 
3 Geb. u. Hallstatt, Supplement, 1902, p. 329. 
4 Or rather from limestone-nodules in the bituminous, marly shales, mostly 
wrongly referred to in literature as ‘‘ Posidonomya Kalk ’’, as has been pointed 
out by Professor Wiman (‘‘ Ein paar Labyrinthodontenreste a. d. Trias Spitz- 
bergens’’: Bull. Geol. Inst. Univ. Upsala, vol. ix, (1908-9), 1910, p. 34). 
Most of the specimens are from ‘‘ Nodule Bed, Base of Trident, Sassendal ”’ ; 
three examples only came from “‘ lowest line of nodules ’’ or “‘ Lowest Lime- 
stone’’ on Mt. Marmier. 
5 “Trias Brach. & Lamell.’?: Mem. Geol. Surv. India, Pal. Indica, ser. xv, 
Himal. Foss., vol. 111, pt. 11, 1899, pl. i, fig. 24. 
