184 GENESIS OF THE ARIETIDA. 
straight, prominent dorsally, but obsolete on the edge of the abdomen. The 
channel ridges have also disappeared, and the channels are only indicated on 
either side of the keel. The keel, however, is persistent. 
The abdominal lobe on the latter part of the ninth volution is somewhat 
more than one half longer than the superior laterals, and the inferior laterals 
one half longer than the superior lateral lobes. This is a senile tendency to 
return to larval proportions, since the proportional adult difference in length of 
the abdominal lobe is at least three fifths. 
A specimen in the Geometricus bed, from Nurtingen, labelled nodosaries, in 
the Museum of Stuttgardt, exhibits the characteristics of this species. Quen- 
stedt’s original of nodosuries shows that the identification of such specimens with 
his nodosaries is not correct. It is very often regarded as the young of Cor. tri- 
gonatum, but is far too much compressed, and whorls too small, though otherwise 
quite similar. 
Wright's figure of an old specimen of this species under the name of Ariet. 
Crossi leaves little room for doubt that it occurs in England with the same 
peculiar form as in Germany. Wright does not mention that there are any 
varieties. 
SECOND SUBSERIES. 
Coroniceras Sauzeanum, Hyarr. 
Plate VI. Fig. 4-14. Plate VIII. Fig. 1-3. Summ. Pl. XII. Fig. 10. 
Amm. Sauzeanus, D’Ors., Terr. Jurass. Ceph., p. 304, pl. xev. fig. 4, 5. 
Amm. spinaries, Quenst., Der Jura, pl. vii. fig. 4; Amm. Schwab. Jura, pl. ii. fig’ 8-14 (fig. 15-17?). 
Localities. — Whitby, Leicestershire, Semur, Salins, Gmiind. 
D’Orbigny’s original specimen, (Plate VI. Fig. 12, 13,) with which this iden- 
tification was made, is smooth probably throughout the first four whorls. The 
centre was obscured, and the exact number of whorls was estimated. The abdo- 
men is flat, with a very obscure siphonal ridge on the fifth whorl. The pile are 
terminated by a tubercle, which is elevated so that it stands on a level with or 
above the abdominal continuation of the pile. These nearly meet, and in some 
specimens actually do cross the siphonal ridge, giving the shell a microceran 
aspect. 
The further development of these peculiarities would lead to a form in which 
the keel would become more distinct, but would be guarded by very shallow 
channels, and in which also the pilw, gracefully curving as in this specimen, 
would terminate in a tubercle standing out prominently on the edge of a flat- 
tened abdomen. Such a form, of which the young is shown in Fig. 10, 11, 
occurs in the same locality, and it is evidently an older individual of this 
species. 
The sutures of this specimen are visible on the third quarter of the sixth 
whorl. The abdominal lobe is shallower -and broader than in variety Gaudryi, 
and the inferior lateral saddles also broader proportionately. The sutures are 
more like those of the young of variety A, Cor. bisnicatum. The edges of the 
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