190 



THE LIAS AMMONITES. 



Fig. 59. — Aegoeeras Davcei, 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 Plantjlati 

 with the CoRONARii. The following are typical species. 



Aegoeeras Davcei, Sow. (fig. 59). 

 — arraatum, Sow. 



Stephanoceras fibulatum, 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. 

 StepTianoceras Blagdeni, Sow. 

 Side view. Front view. 



Fig. 62. 



Fig. 63. 



Stephmoceras 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 Plantjlati. This group is very characteristic of the 

 middle division of the Inferior OoHte 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 



