AMALTHEUS. 243 



times bent outwards or inwards. A simple, corneous anaptychus. 

 Lobes usually strongly incised, siphonal lobe shorter than the 

 first lateral, lobular bodies broadly wedge-shape. 



The development of the Amalthese in the older formations has 

 already been spoken of by Waagen, and we will here only add 

 certain observations on their structural peculiarities, which the 

 genus acquires in the cretaceous times. On one side we find 

 forms in which the lobes are arranged in the normal way, so 

 that after the siphonal lobe, two lateral, and finally several 

 auxiliary lobes succeed each other ; one portion of these species 

 is furnished with very complicated lobes, whilst in others re- 

 duction occurs (Am. Bequienianus), which may go so far as to 

 form ceratiloid lobes (Am. Robini, Thioll., etc.). On the other 

 hand, forms appear in the chalk which differ entirely from the 

 normal law of the arrangement of the lobes, inasmuch as five 

 lobes may intervene between the siphonal lobe on one of the 

 flanks of the whorl to the sutural line. In order to understand 

 this structure, one must remember that in many Jurassic 

 Amalthese the lobular bodies are already become short and 

 broad, so that the three long, slender, terminal branches of the 

 first lateral have attained a certain degree of independence ; 

 besides the external saddle becomes very broad, so that the 

 secondary lobe at its base stands out strongly. Most instructive 

 of all, in regard to the transition of this arrangement to the 

 complete independence and equivalence of all these elements and 

 the complete disappearance of the body of the first lateral lobe, 

 is the arrangement of the sutures in the form from the North 

 German Neocomian, which is cited as Am. Gervillianus, and in 

 Am. Balduri, Keys. 



Of these cretaceous Amalthese with abnormal arrangement of 

 the lobes, there are two groups, viz. : the one has lobes much 

 toothed, and here belong Am. syrtalis, Mort., placenta, Dek., 

 and their allies ; the other presents atavistic reduction of the 

 lobes, which have here also progressed as far as the ceratitic 

 stage (Am. pedernalis, Roem., mbrayeanus, d'Orb.). 



All cretaceous Ammonites with an abnormal number of lobes 

 belong to Amaltheus, as well as the greater part of the creta- 

 ceous Ceratites, of which, however, a smaller portion do not 

 belong here but to Schloenbachia. 



