FIFTH, OR AGASSICERAN BRANCH. 207 
parative Zodlogy, which are so similar to Ast. Turneri that they differ in only one 
characteristic, namely, the shallowness of the umbilicus, due to the gradual 
curvature of the sides. In Ast. Turner the breadth of the dorsum, and the con- 
sequent abruptness of the umbilical shoulders, is a marked peculiarity, even at 
an early nealogic stage. These specimens were in the nealogic stage; if older, 
they would probably also have shown a less amount of involution than in Ast. 
Turnert. This last species becomes generally, though not invariably, larger in 
five volutions than the former in the course of five and a half. Specimens of 
stellare also approximate very closely to As¢. aeceleratum ; they differ, however, in 
the less involution of the whorls, and in other correlative characteristics. 
Depressed tubercles similar to those of the young of ob/usum appeared, in the 
only specimen in which they could be detected, on the last quarter of the second 
whorl, and true pile on the third quarter of the third whorl, earlier by one 
volution than in var. E of oddusum. Thus even in this unimportant character 
acceleration appears to have taken place as it had in other characters. 
There is one specimen of this species in the Museum of Stuttgardt, from the 
Geometricus bed of Géppingen, though it is more common in the Obtusus bed. 
The largest specimen in this Museum reached a diameter of 450 mm. (PI. X. 
Fig. 1, 2). The last whorl was perfectly smooth, the abdomen had become sub- 
acute, and the channels obsolescent, resembling those of the adults of Ast. 
Collenott. 
Asteroceras acceleratum, Hyarr. 
Plate IX. Fig. 4. Plate X. Fig. 3. 
Locality. — Semur. 
The involution covers two fifths of the sides on the sixth whorl, and one half 
of the second quarter of the eighth, whereas in Ast. stedlare the extreme limit of 
involution is one third. The whorl is similar to that of this species, but is much 
broader abdomino-dorsally. The umbilical shoulders are large and abrupt, the 
dorsum much broader than the abdomen, the latter being but little wider than 
the area of the channels. The latter are very broad and shallow, with smooth 
but depressed lateral ridges. The keel is well marked, but depressed as in 
obtusum. The abdomen is therefore quite different from that of either Brooki 
or Turners. 
The young are similar to s/ed/are until a late nealogic stage, and differ only in 
the greater involution of the whorls in later stages, and in the earlier develop- 
ment of the senile folds and trigonal form. The umbilicus could be observed in 
only one specimen. In this the pile: began with coarse folds on the last quarter 
of the second whorl, which developed into true pile on the first quarter of the 
fifth whorl. 
The largest specimen from Semur measured 202 mm., and had completed the 
seventh, and part of the eighth volution. The breadth of the first quarter of 
the eighth whorl measured on the sides was 77 mm. There is a specimen in 
the Museum of Stuttgardt, labelled Amm. stellaris, found at. Gbppingen in the 
