104 GENESIS OF THE ARIETIDA. 
has no tubercles, The specimens are large shells, and afford fine examples of 
the senile stages. Debililatus, Rey., is similar to our lowest transitional forms 
of Conybeart. It may be a direct descendant of this from earlier times, or, more 
likely, a degenerate form. This grades into Landrioti, Rey. (D’Orb.), which is 
simply a more compressed form. 
The occurrence of a form like Arn. falcaries in the Angulatus bed at Semur 
shows that we may anticipate in the future the finding of the radical arnio- 
ceran forms at this level or earlier. It is also very interesting to note that Arn. 
Hartmanm, of the Birchii or Tuberculatus bed, is a morphological equivalent of 
raricostatum, being, with the exception of the young, very similar to that species. 
The more interesting facts shown by this table are as follows. The succession 
of the forms in the schlotheimian series has remarkable regularity, according 
very closely with their genetic relations. The caloceran series, though very com- 
plete in the lower beds, is not so fully represented as in South Germany. Higher 
up in the Birchii or Tuberculatus bed of Collenot, and probably upon the highest 
level at about the time the Raricostatus bed of other basins was being deposited, 
the series had an unusual number of forms. The vermiceran series has a most 
extraordinary display of varieties, but apparently not quite so full a representa- 
tion in the lowest beds as in South Germany. Arnioceras is more fully repre- 
sented in the Bucklandi beds than in any other fauna, and has also many species 
in the higher beds. The coroniceran series has a similar history, but is not more 
fully represented than in South Germany. The agassiceran and asteroceran 
series are also very fully represented, and have the most highly modified species ; 
the absence of Brooki will therefore probably be supplied at no distant day. 
The oxynoticeran series has also a complete history, and probably is nearer 
perfection than is shown in the table, but it nevertheless seems to have had 
no Middle Lias forms. 
Fauna or THE Ruone Basin.— Taste III. 
The basin of the Rhone is equally important with that of Semur, and we give 
below a list of Dumortier’s species and their synonyms in the different horizons. 
Dumortier mentions only Burgundice, and fragments of Johnstoni and planorbis, in 
what he calls the Planorbis bed. This indicates the possible absence of the lower 
beds of this horizon, since this is evidently the fauna of the Caloceras bed. 
The Angulatus horizon has a fauna less rich in species than that of the Cote 
d’Or, especially when one considers the large number of localities from which the 
author’s collections were gathered. The list includes, besides the species given 
in the table, Amm. bisulcatus, a very doubtful form. It may be a form of Cony- 
beari, or similar to the peculiar sulcated form described in the note above on 
page 70, but it is probably not a true Cor. brsuleatum. 
There are no transitional beds mentioned between this and the bucklandian 
horizon, and the beds are evidently not so fully presented, either geologically or 
paleontologically, as in the basin of the Cote d’Or. The list is very meagre as 
compared with that in the corresponding beds at Semur, but the presence of 
