234 PROCEEDINGS COTTESWOLD CLUB 1906 
Pstlonotoceras, Schlotheimza, etc., shews that they are quite 
unconnected with the Arietide. Next P. Adanorbis is most 
unlikely to be the ancestor of the Schlotheimian group 
(Caloceratidz.) for it is a catagenetic species, obviously de- 
clining from the costate stage to the levigate, having nearly 
passed out of the costate stage, in fact. What is wanted 
is an anagenetic species which is passing from the levigate 
to the costate—the morphic equivalent to Arnzoceras 
semicostatum ; earlier than that, an anagenetic smooth 
species, equivalent to the Arietidan Arn. miserable ; earlier 
again asmooth globose species, equivelent to the Arietidan 
Cymbites. Out of the Arn. semicostatum equivalent 
would come an anagenetic costate species, equal to C. 
JSohnstont,; and, out of such a form, the Caloceratide 
could be developed. Only, C. /ohustonz itself cannot be 
placed as such an ancestor, because it is later in date than 
Pstilonotoceras ; a C. Johnstont morphic equivalent is the 
ancestor. ; 
Similarly with the Arietide, Cymdztes, Arn. miserable, 
Arn. semicostatum indicate the anagenetic stages leading 
up to Coroniceras ; but they are not the actual ancestors, 
as they occur later: it is their morphic equivalents— 
species with the same simple, not dependent suture-line’ 
—that are the actual ancestors. 
Then Asteroceras is not an anagenetic series, but a cata- 
genetic one, going from tuberculate (= Coronzceras) as 
the inner whorls of Ast. obtusum shew, to the costate. 
The more tuberculate ancestor of Ast. obtusum is figured 
by Wahner as Arvetites stelleformis, Giimbel." 
Another Arietan genus, Oxynotoceras, is a highly accele- 
rated catagenetic series, mainly in the levigate stage. 
1 Zonen des Unt. Lias; Pal. (Est.-Ungarns, vol. vi, (4) Pl. xlv, fig. 2, 1888. 
