188 



THE LIAS AMMONITES. 



Harpoceras serpentinutn, Sehlotheim (fig. 54). 



— radians, Reinecke. 



— bifroiis, Bruguihre. 



Harpoceras insigne, Sdtuhler. 



— thouarsense, cCOrhigt^y. 



— opaliunm, Reinecke. 



III. Amalthei. — The sickle vanishes, the radii have a very long stem, which bends 

 only near the siphonal area, becoming here very prominent. The 

 margin is sharp, the keel often divided by the folds as if into scales. 

 The siphonal lobe is here also much shorter than the upper lateral, 

 and its wall ascends obliquely up to the siphonal saddle, but not 

 by any means so obliquely as in the Falciferi. The upper lateral 

 is very broad, almost as broad as it is deep, so also is the under 

 lateral. The saddles, as well as the lobes, are extensively foliated, 

 so that in these lobes large and wide outstretched processes are 

 formed in the middle of the saddles, with very deep secondary 

 lobes. The points of the dentations do not hang down, but in 

 general stand perpendicularly upon the axis of the lobes. By this means the sides of 

 AmaltJieus in all the species, even when the shell is wanting, have an especially foliated, 

 incised appearance, in which great intricacy appears to prevail. Notwithstanding, with 

 some attention we easily, even to the least detail, find the ever-repeated symmetry as well 

 in the individual points as in both sides of the whorls. These Ammonites are much 

 inclined to become involute. The family ascends from the Lias up to the Coralline 

 Limestone of the Middle Oolite, and each intermediate formation possesses its own 

 special forms. The following are typical species from the Lias and Coral rag. 



Fig. 55. — AmaltJieus cordatus. 

 Sow. 



Amahheus margaritatus, Montfort. 



— Guibalianus, d'Qi-bigny, 



— Greenhoughi, Sowerby. 



Amaltheus oxynotus, Qiieixstedt. 



— spinatus, Binguiere. 



— cordatus, iSoioe^-iy' (fig. 5.5); 



IV. Capricorni — This group connects itself very closely with the Amalthei, 

 From AmaltJieus margaritatus, through Amal. cordatus, Amal. Lamberti, and Amal. 

 ODijjltaloides, we arrive at Aeg. capricornmn. The scales upon the keel of these 

 Ammonites have even raised themselves higher, and are first bent 

 forward, then become broad folds with a point before. Ihe siphonal 

 area of the Capricorni is broad, often broader than the sides. The 

 siphuncle is not specially prominent, the ribbing of the folds 

 on the sides is in general unusually strong, always single, even on 

 the back ; without much flexion, and rarely Avith knobs or spines 

 upon the sides. The siphonal lobe in general goes out perpen- 

 dicular with vertical walls. The lateral lobes are, as in the 

 Amalthei, less deep than broad, and often at their bases are 

 broader than at the mouth, they are all very slightly or almost not 

 at all involute. The following species are typical forms. 



Fig. 56. — Aegoceras capri- 

 cornuni, Scljlotli. 



