= een 
FIFTH, OR AGASSICERAN BRANCH. 195 
the prolonged existence of the goniatitic proportions, which are generally con- 
fined to nzpionic stages of growth in other Ammonitinw. They are also very 
similar in some of the nealogic and adult stages, both in form and characteristics, 
if we except the sutures, to Psiloceras The sutures acquire the deep arietian 
abdominal lobe quite early in life. The sutures of the higher species, Agass?- 
ceras Scipionianum, are very similar to those of Coroniceras. The affinities of 
Agas. levigatum and Ast. obtusum, and also those with Psiloceras, have been fully 
discussed elsewhere.” In the clinologic stage the abdomen becomes more acute, 
and the sides smooth. Neumayr has lately redescribed this genus in part 
under the name of Cymbites.’ 
Agassiceras levigatum, Hyarr. 
Plate VIII. Fig. 9-14. Summ. PI. XIII. Fig. 1. 
Amm. levigatus, Sow., Min. Conch., pl. 570, fig. 3. 
Amm. levigatus, Orr., Die Juraf., p. 81. 
Amm. abnorme, Haver, Unsymm. Amm. Ilierl.-Schich., Sitz, Akad. Wien, XIII. pl. i. fig. 11-17. 
Cymbites globosus, Geyer, Ceph. Hierl.-Schich., pl. iii. fig. 26. 
Localities. — Lyme Regis, Semur, 
This species has an exceedingly immature or nepionic form. It seems 
frequently to complete its growth in five whorls. The aperture has a simple 
pointed rostrum, the lateral edges slightly flaring, with a broad shallow constric- 
tion, Pl. VIII. Fig. 12, very similar to the aperture of Oppel’s type of Amm. pla- 
norbis The living chamber is about one half a volution in length. 
Var. A, Plate VII. Fig. 11. This is smooth during four volutions, and the 
pilze, if present, are developed only on the last whorl. The whorls are more 
compressed than in other varieties, and the umbilicus not so deep. 
Var. B, Plate VIII. Fig. 9, is smooth only during the first three or three 
and a half whorls, and then has immature folds like those of var. plicalum of 
Psil. planorbe. The younger whorls are wider than in other varieties, and the 
umbilicus deeper. 
Var. C has the pila much more distinct, but the period at which they appear 
is the same as in the preceding variety. The pile are apt to cross the abdomen, 
forming slight ridges. This, like all other characteristics, is found more or less 
also in other varieties. 
Var. D, Plate VIII. Fig. 10-12, is founded on the presence of a faintly 
defined siphonal ridge. This includes members of other varieties, regardless of 
the time at which the pile are developed, their greater or less prominence, and 
1A paper by E. Haug, “ Ueber Polymorphidae,”’ Neu. Jahrb. Mineral., 1887, II. p. 92, gives an in- 
teresting account of this genus, in which he substantially agrees with our descriptions, but insists upon the 
keelless character of the whorls, If we are correct, this is an adventitious character common enough in 
dwarfed forms, or arrested development in some individuals or in the varieties of the same species, but a 
variable within the species, and not a generic character. 
2 See pages 65, 66. 
3 Jahrb. Geol. Reichsans., XX VITI., 1878, p. 64, note. 
4 We have studied Oppel’s type of this species, and found that Oppel’s figure gives the lateral curves 
of the aperture in an exaggerated form, and the constriction too deep. The real aperture is therefore more 
like that of /evigatum than it appears to be in his figure. : 
