102 GENESIS OF THE AKIETIDiE. 



which convinced me of the derivation of that species from Agassiceras, was found 

 in 1873 in the Stuttgardt collection. The specimens of the last named species 

 had been selected by Professor Fraas out of several barrels of specimens of the 

 same species gathered in the same locality. I looked very carefully in all other 

 collections, handling hundreds of specimens, without finding any duplicates of 

 these forms. 



Hauer has given, in his "Nordostlichen Alpen," ' an involute form, apparently 

 the same as Oxyn. Lymense, and figures of the young, which are, however, in part 

 distinct. 2 His Amm. Greenoughii is evidently a member of the same subseries, and 

 identical with the more involute forms of Amm. Guibalianus of Reynes. This sub- 

 series is only sparsely represented in the Northeastern Alps, and its date of 

 appearance is not yet settled. 



The collection at Semur has this species in the Birchii or Tuberculatus bed. 

 M. Collenot states that this bed in the Cote cl'Or basin contains the same spe- 

 cies and is equivalent to the Tuberculatus, Obtusus, Oxynotus, and Raricostatus 

 beds of South Germany and England, and that it is not possible to separate the 

 faunas, as has been clone elsewhere. The appearance of the usual forms of Oxyn. 

 oxynotum in great abundance in Southeastern France according to Dumortier, and 

 also of Oxyn. Simpsoni and Lymense, shows that the last named forms may have 

 made their first appearance in France. This is further substantiated by the fact 

 that Oxyn. Lymense, according to Wright, is found more abundantly in the South 

 of England than in the midland counties. The appearance of Oxyn. oxynotum 

 and Lymense in the basin of the Northeastern Alps can be accounted for by cho- 

 rological migration, in the same way that we have accounted for the presence of 

 Asteroceras and others in that basin. The radical species, oxynotum, is cited by 

 Schlonbach 3 from only one locality in North Germany, and is not mentioned at 

 all by Dr. Brauns in his " Unterer Jura nordwestlichen Deutschland," or by 

 Emerson. 



The second subseries of this genus is completely represented in the fauna of 

 France. Three species only are found in England, none in South Germany, and 

 two in the Northeastern Alps. Apparently none have been found in North Ger- 

 many 4 or Luxemburg. The collections at Semur contain a nearly complete 

 series of forms, and Dumortier has added others occurring in the Rhone basin. 

 The home of the series, therefore, appears to have been in the Cote d'Or or 

 Rhone basin. 



This is the only series of the Arietidse which overstepped the boundaries of 

 the Lower Lias. Other species have been reported by various authors as occur- 

 ring in the Middle Lias, especially the Jamesoni bed ; but these were found asso- 



1 Denkschrift. Acad. Wien, XI., pi. xiii. fig. 6, 7. 



2 Fig. 6, 7, appear to us to belong to some species of the second or Greenoughi subseries. 



a Eisenst , etc., Zeitsch. deutsch. geolog. Gesellsch., XV., 1863, p. 502. Amm. qffinis, however, de- 

 scribed in Paleontogr., XIII. p. 170, pi. xxviii. III. fig. 1, by the same author, is from Middle Lias, Greene, 

 Brunswick, which is very similar to if not identical with Oxyn. oxynotum. We have not cited it in the 

 table, however, since it may prove to be more nearly connected with Oxyn. Oppeli than with oxynotum. 



4 Schluter describes Oxyn. Oppeli of the Middle Lias as occurring at Altenkirchen and Borlinghausen in 

 the Teutoburger Wald, and Schlonbach describes and figures the same from Amberg. 



