JAMES PEBRIN SMITH 11 



back in the ontogeny of Tropites, until it appears in the larval stage, as- 

 sociated with septa like those of the Devonian Afiarcestes, and form and 

 sculpture like that of the Carboniferous Gastrioceras. The ontogeny 

 of Tropites is shown on PI, IV, ligs. 11-21, where it may be compared 

 with the simpler development of Columhites. The ontogeny of the 

 ancestral Goniatites is shown on PI. I, figs. 1-9. 



In a like manner, in the development of Clioniies, (PL XV, figs. 

 1-12), the ventral furrow, which is a late or coenogenetic character of the 

 group Trachyceras, is accelerated in inheritance until it appears in asso- 

 ciation with characters belonging to genera far below Trachyceras in the 

 series. The term, "telescoping," which has been applied by Grabau to 

 this phenomenon is graphic, but hardly accurate enough for use in 

 strictly scientific nomenclature. 



Fixed Types. 



The first step towards degeneration is cessation of progress, seen in 

 the case of all persistent types. Such types may become finally "left 

 overs," fixed in the ancestral characters, anachronisms, or "contempor- 

 ary ancestors." They usually become dwarfed, or at least seem so, for 

 they retain the small size of the ancient forms, of which they are the 

 unmodified, or little modified descendants. Such types among Ammon- 

 ites are Lecanites and Nannites, which persist until the Middle Triassic 

 with the characters of Devonian and Carboniferous genera. (See PL III, 

 figs. 1-3, PL III, figs. 4-8, for the characters of these genera). These dwarf 

 genera are represented by few species at any time in their later history, 

 showing by their very fewness the lack of that virility which is character- 

 istic of progressive forms. Their ancestors, the Goniatites, and their con- 

 temporary kinsfolk, the highly specialized Ammonites, are both charac- 

 terized by abundance of individuals, species, and genera. Nannites and 

 Lecanites are "poor-relations," few, small, and unimportant, though won- 

 derfully interesting, for they give us an insight into the beginning of the 

 phenomenon of degeneration. 



Stretching the Ontogeny, 



The next step towards degeneration consists in prolonging the on- 

 togeny, as when a specialized group remains longer in the larval and 

 adolescent stages than did its ancestors, while finally reaching to the full 

 perfection that they had attained. The best example of this is seen in 



