FIFTH, OR AGASSICERAN BRANCH. 197 
Several specimens of this species in the Stuttgardt Museum, Upper Bucklandi 
bed, from Balingen, showed living chambers, as pointed out to me by Professor 
Fraas, always much shorter than in planorbe, and the sutures distinct. The 
peculiar folds appearing on some shells, and the form and aspect of the whorls, 
like those of the nealogic stages of Scipionianus, show that their affinities are in 
the direction of this species. The examination of the originals of Quenstedt’s 
descriptions from Pforen fully sustained the above, and a fine suite of the same 
species at Semur, in the corresponding horizon, exhibited several forms transi- 
tional to the young of Seinonianus. 
Professor Misch, in the Museum of the Polythenic at Ziirich, showed me 
several specimens of striaries, in which the keel was so faint as to be hardly per- 
ceptible, and the striations no better marked than in Psiloveras. These were 
named psilonotus, and were found at Salins associated with typical striaries. The 
apertures are also similar to those of Psi. planorbe. 
Agassiceras Scipionianum, Hyarr. 
Plate VII. Fig. 11-15. Plate X. Fig. 11-13. Summ. Pl. XIII. Fig. 7%. 
Amm. Scipionianus, D’Ors., Terr. Jurass. Ceph., p. 207, pl. li. fig. 7, 8. 
Amm. Scipionianus, Quenst., Amm. Schwiib. Jura, pl. xiv. fig. 1-3 (not pl. xvil.). 
Ariet. Scipionianus, Wricut, Lias Amm., p. 289, pl. xiii. fig. 1-3; pl. xix. fig. 8-10. 
Localities. — Whitby, Semur, Arton in Luxemburg, Gmiind. 
This species varies exceedingly. Some of the young show a crenulated keel, 
and they may also be either smooth or pilated on the sides. The abdomens are 
keeled, and occasionally, though very slightly, channelled. The form of the 
whorl in the young may be either very gibbous, Plate VU. Fig. 11, 12, or com- 
paratively compressed. The pil also vary from comparatively thin and depressed 
to prominent and well defined, with or without tubercles; they may also be very 
numerous or few in number, and be very distinct, or thick, awkward-looking 
folds. It has been commonly supposed that the true affinities of this fossil were 
with the margaritatus group, but its development is altogether peculiar, and its 
sutures are distinctly arietian. There are two varieties of this species with dis- 
tinct nealogic stages but similar adults; one, as described above, very gibbous 
and heavily pilated,’ and another more compressed at all stages, and approxi- 
mating to Agas. nodosaries.” The latter may be identical with Agas. nodosaries, 
or it may be distinct; the materials at hand are not sufficient to determine this 
question. 
In old age the tubercles are suppressed, the sides become flatter and more 
convergent, the genicula bend less abruptly and curve slightly forward, the 
channels disappear, but the keel remains very prominent and sharp. The clino- 
logic stage just before the pile become obsolete is very similar.to the adult of 
Ast. Collenoti, but the shell is not so involute. 
The young of this species has the gibbous volutions so characteristic of devi- 
gatum and striaries. The sides are at first divergent, but they become nearly 
i-Plate vii fig. 11,125 ple x. fig, 21, tz. 2 Plate x. fig. 13; pl. vii. fig. 15 
