POLYMORPHITES. 267 
der ersten Jugend sind die Rippen auf der Externseite durch ein vertieftes, ebenes 
glattes Band scharf unterbrocken."^) It is very probable, therefore, that a later 
species than Pol. Zitteli was a common ancestor of Tmetoceras and Gatulloceras. 
The three genera, Polymorphites, Tmetoceras, and Gatulloceras, are easily 
distinguished by external characters. Polymorphites has ribs crossing the abdomen, 
Tmetoceras has a sulcate abdomen, and Gatulloceras has a carinate or a carinate- 
sulcate abdomen. It is interesting to consider that these three copy in their 
development certain Lower-Lias genera. For instance, it would not be amiss 
to say that Polijmorphites is the morphological equivalent of Waehneroceras, 
Tmetoceras of Schlotheimia, and Gatulloceras of Galoceras or Vermiceras. 
PoLYMOEPHiDiB {continued). 
Genus — Poltmoephites, Siitner. 
{Type — PoLTMOEPHiTES POLYMOEPHUS, Quenstedt sp.) 
— PoLYMOBPHiTES, Sutner, in collection {teste Haug). 
1887. PoLXMOBPHiTES, Haug. ' Polymorphidse ;' Neues Jahrbuch £iir Mineral., 
&e., Band ii, p. 120. 
Compressed, generally e volute, uncarinate, or sub-carinate. Whorls orna- 
mented with annular radii,^ which cross the abdomen without interruption by 
carina or sulcus. Suture-line simple. 
1 have only one species to describe, but it is necessary to explain why I place 
it here. Commencing with Pol. polymorphus — a smooth form — continuing to Pol. 
polymorphus lineatus — with strias, — and to Pol. polymorphus costatus — striae 
enlarging into ribs, there seems to be a definite phylogenetic series characterised 
by the retention of a primitive style of ribbing — the " uninterrupted annular." 
Such is the character of the later-appearing species " Veimosse ; " and from this 
comes " Zitteli,'" in which periodic constrictions are introduced — but this is a side 
shoot. However, in the direct line from " Vernosse^' there is "norma," a small 
species with inflated whorls, and also my species " senescens " with compressed 
whorls. 
This phylogenetic series passed through a period of growth up to " Vernosse '* 
or " Zitteli," and shows unmistakable old age in " senescens." Its primitive 
ornamentation marks a radical stock ; and, moreover, a stock from which 
^ ' Cap san Vigilio ;' k.-k. geol. Eeiehsanstalt, Bd. xii, No. 3, p. lOi, 1886. 
2 Straight radii which appear like rings on the whorl. They may cross the abdomen or be more 
or less interrupted by a carina or sulcus. Subannular radii might not be quite straight, or might be 
slightly drawn forward on the ventral area. 
