190 
THE LIAS AMMONITES. 
Fig. 59. — Aegoceras Bavm, Sow. 
VI. DoRSATi. — The broad siplional area is united with the 
sides almost at a right angle. A series of simple tubercles extend 
round near the margin, through which the simple lateral folds 
become divided into double ones, before crossing the area. The 
siphonal area is always smaller than the sides, whereby most of 
the species preserve a tolerably discoidal form. The auxiliary 
lobes often extend obliquely against the upper lateral, although 
not in all the species. The Dorsati unite the Planulati 
with the CoRONARii. The following are typical species. 
Aegoceras Davcei, Sow. (fig. 59). 
— arraatum. Sow. 
Stephanoceras fibulatura, Sow. 
— Brocchii, Sow. 
VII. CoRONARii. — A well-marked series of tubercles so widens the siphonal area 
that it becomes wholly flat, and a good deal broader than the sides. The sharp, wide, 
forward-directed folds become divided by the tubercles, the whorls are much involuted and 
Fig. 61. 
Stephamceras Blagdeni, Sow. 
Side view. Front view. 
Fig. 62. Fig. 63. 
Stephanoceras Braikenridgii, showing labial prolongation. 
Side view. Front view. 
proportionally short, and form a deep umbilicus. The upper lateral lobe stands always 
above the tubercles, the under lateral beneath. By this character they are readily, and 
with greater certainty, distinguished from other forms. The siphonal lobe is longer than 
the upper lateral ; and there are several auxiliary lobes, which in their form and position 
entirely resemble those of the Planulati. This group is very characteristic of the 
middle division of the Inferior Oolite as the following species demonstrates. 
Stephanoceras Humphriesianum, Sow. 
— Brongniartii, Sow. 
— Brocchii, Sow. 
Stephanoceras Gervillii, Sow. 
— Blagdeni, Sow. (fig. 60). 
— Braikenridgii, Sow. (fig. 62). 
VIII. Macrocephali. — The increase of the whorls is unusually rapid, especially in 
the breadth of the mouth. The siphonal area and sides are joined imperceptibly together 
