104 GENESIS OF THE AKIETID^E. 



has no tubercles. The specimens .are large shells, and afford fine examples of 

 the senile stages. DebiUtatus, Rey., is similar to our lowest transitional forms 

 of Cow/bcari. 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 Am. 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 Am. 

 Hartmanni, 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 fticts 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 Broolti 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 of the Rhone Basin. — Table 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. bisidcatus, 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. bisidcahim. 



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 



