ee ae 
201 
Fourth Section—Invouvrtt. 
Shell highly involute; inner whorls sometimes almost entirely 
concealed. Shell during middle age undergoes a great change 
of form; in others the involution is less, and the umbilicus 
becomes wider. Aeg. Henleyi, Sow.; Aeg. striatum, Retnecke ; 
Aeg. Bechei, Sow.; Aeg. curvicornum, ScHtoEns.; Aeg. pettos, 
QueEnst.; Aeg. heterogenes, Youne. 
All the forms of this section are from the Henleyi zone of 
the Middle Lias. 
This genus begins in the Muschelkalk zone of Arcestes Studer 
with A. incultum, Bryr., A. Palmai, Moss., A. Buonarottii, Moss., 
and became extinct in the Middle Lias. 
Genus Artetires, Waag.—Shell discoidal, with a wide umbi- 
licus; the sides of the whorls covered with straight simple 
ribs, Which often have tubercles developed on them near the 
Mg 
Fia. 55.—Arietites obtusus; Fia. 56.—Section of Arietites 
Sow: Front. obtusus, Sow. 
Q 
