58 GENESIS OF THE ARIETIDAL. 
catenata in varieties having the most discoidal forms and the pile crossing the 
abdomen without a channel would throw some light on this problem, we begged 
Professor Emerson to give us some specimens of this species from the Markolden- 
dorf basin for examination. After making several preparations of those kindly 
sent in reply to this request, the inner whorls and all stages up to the adult were 
studied. The young to the diameter of 6-8 mm. resemble closely the older 
nealogic stages of Wehn. curviornalum' and circacostatum, as figured by Wihner.? 
The pile are slightly bent forward on the abdomen, are fold-like, as in Psiloceras, 
and without the sharp bend and tongue-like forward projection which are the 
primitive indications of a tendency to form a median ventral channel. This 
tongzue-like projection is formed in the next stage, and the pile, which have in 
the mean time become very sharply defined and prominent on the sides and 
abdomen, also exhibit a slight flattening or decided depression, in most forms, 
along the median line of the abdomen. It is evident from these facts that 
Wiihner was right in considering the species of the waehneroceran series as tran- 
sitions to Schlotheimia. 
Caloceran Series. 
This series is divisible into two subseries. 
First Subsertes.--The direct connection of the plicated variety of Psil. 
planorbe with Caloceras Johnston (torus, D’Orb.) has long been insisted upon by 
Quenstedt, and in his collection the intermediate types are found. There is 
(1) a plicatus with whorls slightly narrower dorso-abdominally than is usual in this 
variety, and somewhat more prominent folds; then (2) one with the same form, 
but still narrower dorso-abdominally, and for this reason with a blunter and 
rounder abdomen; then (3)* a young one of this form precisely similar to the 
Johnston. These show that Johnston’ is an offspring of the plicated p/lanorbis, in 
which the more gibbous sides, narrower whorls, and rounder, broader abdomens 
of the young of that form are retained throughout life. 
From Johnstoni one can pass by gradations into Caloceras tortile* First, the 
typical ¢ortile, with young until a late stage, having rounded abdomens and the 
aspect of the narrower and smoother forms of Johnston. These become angular 
on the abdomen at various ages, without producing a true keel. Secondly, those 
which introduce a slight keel upon the elevated abdomen, but which subse- 
quently disappears in the increasing angularity of the abdomen in the senile 
stages. Thirdly, those which introduce a keel, then a squared or quadragonal 
form of whorl, like that of Caloceras laqueum. Fourthly, those which are of very 
large size, similar in all their stages, except in the angular abdomen, to the 
stouter forms of Jo/nstoni, and like these becoming rounded in extreme old age. 
The first variety grades into Cal. Lvasieum, which has rounded, gibbous 
whorls in the young. This has a keel only at a very late stage, or may not 
1 Summ. Pl, x1. fig. 7. 
2 Unt. Lias, Mojsis. et Neum., Beitr., XII., Pl. xv., xvi. 
3 The larger one (2) was fortunately a broken specimen, and showed precisely the same form as (3) in 
the young. 
4 Summ, Pl. xi. fig. 14; Pl. i. fig. 12-14. 
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