

350 me. l. r. spath ox the [Dec. 1914, 



but did not become a conspicuous element of the fauna until the 

 ornamented forms had died out. 



The latter seem to have displaced the unornamented forms 

 altogether in the southern regions ; but, even in England and in 

 France, the group became extinct in rnargaritatus times. The 

 exceptional character of the extreme ornamentation, such as occurs 

 in Tr. ibex in the persistently smooth stock of the Phylloceratidse, 

 may account for the rapid and earlier extinction of the sculptured 

 forms. 



The interrelations of the various forms belonging to the genus 

 Tragopliylloceras might, then, be graphically represented as 

 follows : — 



Margaritatus Horizon. 



Algovianus Horizon. 



Bechei Horizon. Loscombi 



(ambiguum). 



t „4-„„~ a 4-„ tt™,;.,™ ^ Weclisleri-ibex and 



Latecosta Horizon. ! . . .. J „ 



: intermediate forms. 



Ibex-Valdani Horizon. Elteni. \ x ^ 



\ 'Nu.nii^mnlp.. / ^-"^ 



Jamesoni Horizon. 



t 



IV. Phylogeny. 



Futterer. who established the formenreihe of PhyUoceras 

 loscombi, had already traced Tragopliylloceras back to Mono- 

 pl/yllifes, particularly to the group of M. splicer opliyllus. He 

 based his arguments chiefly on the external characters of the 

 shell, considered the ornament a modified monophyllitic one, and 

 dealt with the (adult) sutures which, in his opinion, showed 

 a gradual transition, especially in the development of a trifid first 

 lateral lobe from the original bifid lobe. The immediate attach- 

 ment of the Carixian genus to Triassic forms, without considera- 

 tion of the allied genera that existed in the enormous time-interval, 

 was. however, scarcely convincing. Pompeckj doubted the correct- 

 ness of Futterer 1 s theory, but expressed no opinion himself. 



The latest forms of Monophyllites mentioned by Futterer, and 

 therefore the more or less direct ancestors of the lineage, were 

 Monophyllites aonis Mojs., and M. simony i Hauer. Now. Futterer 

 left Ammonites loscombi in the genus Phylloceras, and, if Phyllo- 

 ceras be the descendant of Diseophyllites (as is generally supposed, 

 and as seems to me probable), the genus Tragophylloceras is at 

 once removed from the Jurassic Phylloceratidse ; for Diseophyllites 

 is a branch of the original Monophyllites root-stock which is 

 distinguished already at the horizon of the above-mentioned 

 31. aonis and M. simonyi by bifid saddle-endings. 



