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94 GENESIS OF THE ARIETIDA. 
The radical ferm Schlot. eatenata appeared in the Planorbis horizon, according 
to the collection at Semur, and in this fauna the successive forms of the schlo- 
theimian series succeed one another without a break in their gradations. Quen- 
stedt’s work on “ Die Ammoniten des Schwabischen Jura” shows that in South 
Germany the series may be complete in numbers of forms, and even more re- 
markable in the size of specimens, and the whole series except Boucaultianus 
appeared before the termination of the Angulatus fauna. There is also a speci- 
men referred doubtfully even to the “ gelbe Sandstein” of the Rheetic beds near 
Tiibingen, thus carrying the possible origin as far back as in the Northeastern 
Alps. If, as we have supposed, Wekhn. subangulare is found in South Germany, 
the evidence becomes still stronger that this was the probable centre for the 
chorological distribution of the group in Central Europe. 
Schiot. angulata and catenata are very numerous in North Germany; but there 
is a notable tendency to the production of smaller specimens in the collections 
we have seen. Schliiter, in his “ Schichten des Teutoburger Waldes bei Alten- 
becken,’’' states that Amm. angulalus, Moreanus, and Charmassei occur there, but 
that the latter is never so large as in South Germany. 
Terquem, in his “ Province de Luxembourg et de Hettange,” ? mentions Amm. 
anguiatus as occurring in abundance, and of good size, but no species like Char- 
masse or Leigneletii. Chapuis and Dewalque give figures of Schlot. angulata, which 
show that the species is similar to cadenatus in having discoidal whorls and 
the pile crossing the abdomen. This species is evidently similar to that from 
Markoldendorf, described by Emerson. Seebach, in his “ Hannoverische Jura,” 
declares that in North Germany there has so far been found only the Amm. angu- 
latus (equal to depressus, catenatus, and Moreanus), and denies the existence of 
Charmasset. Brauns, in his “ Untere Jura im nordwestlichen Deutschlands,” cites 
both angulalus and Charmasset. 
The whole series, including radical, discoidal, and involute species, appear to 
have come into the Northeastern Alps basin first, and to have reached in this 
locality their highest development in discoidal forms. Thence they seem to 
have spread somewhat later in time into the Angulatus horizon of the South 
German basin, and migrated still later to the Cote d’Or and England. In the 
first two basins they reached their highest development in involute forms, — 
a fact which strengthens the impression that the series must have originated in 
the Mediterranean province, since the involute forms are the descendants of the 
discoidal forms. That they arrived in the Cote d’Or later than in South Ger- 
many is shown by Tables I. and II., in which we find Charmassei appearing in the 
Lower Bucklandi zone instead of the Angulatus zone, and by the presence of 
two new and more highly modified species, D’ Orbigniana and Boucaultiana, which 
have not been found in South Germany by any collector up to the present day. 
These views are further sustained by the fact that the English fauna possesses 
only a slender representation of the group, all the species being rare, and occur- 
ring at about the same time as in the Cote d’Or, except Boucaultiana, which is 
1 Page 42. 2? Mém. de la Société Géol. de France, V. 
3 Descrip. Foss. Terr. Secon. de Luxembourg. 
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