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 Scipioniaims, 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 Scipionianus. 



Professor Mosch, in the Museum of the Polythenic at Zurich, 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 Psiloceras. These were 

 named psilonotus, and were found at Salins associated with typical striaries. The 

 apertures are also similar to those of Psil. planorbe. 



Agassiceras Scipionianum, Hyatt. 



Plate VII. Fig. 11-15. Plate X. Fig. 11-13. gumm. PI. XIII. Fig. 7. 



Amm. Scipionianus, D'Orb., Terr. Jurass. Ceph., p. 207, pi. li. fig. 7, 8. 



Amm. Scipionianus, Quenst., Amm. Schwab. Jura, pi. xiv. fig. 1-3 (not pi. xvii.). 



Ariel. Scipionianus, Wright, Lias Amm., p. 2S9, pi. xiii. fig. 1-3; pi. 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 VII. Fig. 11, 12, or com- 

 paratively compressed. The pilte 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, 1 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 geniculse 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 pilse 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 Icevi- 

 gatum and striaries. The sides are at first divergent, but they become nearly 



1 Plate vii. fig. 11, 12; pi. x. fig. 11, 12. 2 Plate x. fig. 13; pi. vii. fig. 15. 



