

RADICAL STOCK. 



Ptibetnu caKpfylhm, u Bupposed by Neumayr, may have been the radical 

 lal ami smooth form from which PtiLpU i nated. It is a \ei\ 



ally of this species, differing only in the sutures, and these, like those of other mem- 

 is in the Northeastern Alps, are phylliform, and have, as we have 

 Although we are disposed to Bhare Neumayr's opinion 

 that P hyllum is the radical of all the Arietidse, we think. nevertheless, 



that the evidence of the forma and Butures favors the theory that the Levi* 

 of the Central European province all sprang from PsS. phnorbe. The sul 

 the normal ArietidsB of Central Europe bave leaa complicated margins than those 

 loceras and Caloceras of the same province; but these in turn are as a rule 

 omplex than those of the same genera in the Northeastern Alps. The 

 Arieticue, therefore, can be characterized as having degenerated in reaped to 

 the sutural margins of the septa. The degeneration of the Butures in /' 

 phmorit and in Cat. lagueum and Verm, sj ibles one t" Bee that this 



tendency i J even in the Plicatus Stork; and it ia probable 1 that the 



Flicatus Stock, with the exception of Vermiceras, all originated in the North- 

 i Alp-^ from Pail, caliphylhm. 

 Tin- degeneration of tin- Butures i> due to an arrest of development followed 

 by tin- retention of uealogic character-, ami i- purely degenerative. This ia, 

 however, accompanied by the evolution of o new character, an increase in the 

 depth and narrowness of the abdominal lobe, in the typical Arietidse. 



PLICATUS STOCK. 

 Wajhneroceran Series. 



interesting forma discovered in the Mediterranean province, and de- 



\\ Lbner in his u Unter i I. - J show that the closest affiliation 



- ami the schlotheimian group. The ^■nn< Washne- 



■ d farther ..i). contains Bpecies like Wcchn ■ than, curvi- 



/ . which ate transitional between Schlotheimia and the true 



plicab 



Schlotheimian Series. 



In this aeries* the number of forms having the pilse crossing the abdomen 

 with a peculiar forward bend, especially in v enable tin 



that a direct connection by transitional forms must have occurred 1" I 



this and W.eln Tie- similarities are. however, not so i low 



is, mid one i- -'ill left n doubt « 

 - tc.ik place in an earlier formation than that of the 

 • d. <t in that ' ng that thi 



