200 GENESIS OF THE ARIETIDA. 
this species. His specimen as figured is, however, younger, and consequently 
less involute, the pile are without tubercles, and the general aspect similar. His 
shell was, according to his figure, notably more involute than Sepiomanus, and 
this agrees also with a specimen in the Museum of Comparative Zodlogy. This 
last is larger than that figured by Quenstedt, and, though comparatively senile 
and quite smooth on the outer whorl, is more involute than any specimen of 
Scipionanus and has a more compressed and more acute whorl. My notes taken 
at the Museum at Semur say, “ the Scipionis of Reynés is only a less involute form 
of Scipionianus,” but it is probable that the specimen observed at Semur may have 
been exceptional, and either extremely old or a pathological example. 
Geyer, in his Liass. Ceph. Hierlatz b. Hallstadt, mentions Cymbies globosus, 
Plate ILL. Fic. 26, a young form of Agas. levigatum, as cited above, and also an’ 
8 ,ay g uh AY ’ ; 
briet. indet., Plate IIT. Fig. 18, which, if not a specimen of Agas, Scipionanum, is a 
very close ally. These are small shells, as is usual in that locality. 
The Afgoc. Cocchi, Canav., Unter. Lias v. Spezia, Plate XIX. Fig. 11, may be 
a young specimen of NSeipionianum, but we cannot venture to refer it to this 
=o) ih ? 
genus. 
ASTEROCERAS. 
The form of the whorl is noticeably less discoidal than in the preceding series, 
except in Ast. obtusum. The abdomen in adults is usually narrower, the sides are 
flatter and more convergent, as well as broader, than is usual in Coroniceras. The 
involution is not limited to the abdomen, and the whorls tend to grow inwards, 
covering more or less of the sides. The pile are fold-like, bending forward on 
to the abdomen, and in most species smooth and without genicule. The young 
have very stout gibbous whorls with divergent sides, which become more and 
more convergent in the nealogic stages, and remain so throughout life. The keel 
is constant in all the young and adult specimens, but the channels are often very 
shallow, and sometimes absent. 
The sutures have a deep abdominal lobe, but the lateral lobes are apt to be 
short and pointed, and the saddles broad. They are similar to those of Coroni- 
ceras, but the marginal lobes are rarely so long as in that genus. In old age the 
abdominal lobe and the lateral lobes and saddles are of about the same length, 
but become broader proportionally, the inferior lateral saddles become shallower, 
and this occurs also in many dwarf forms, which of course are prematurely 
degraded. These senile changes are more marked than in Coroniceras, though 
the old age is not otherwise noticeably different. The genus with relation to 
other genera of the Arietide is notably geratologous, or in other words the shells 
exhibit characteristics similar to those of the senile stages of Coroniceras, and these 
characteristics may be reproduced in the adult, and even in the nealogic stages. 
Each species and individual, however, also has a senile stage in which decline is 
manifested unmistakably, and during this stage the whorl becomes still more 
tna Seca 
