OXYNOTICEEAS. 101 



does possess Ast. acceleratam, a form found nowhere else except in the Cote d'Or. 

 Quenstedt's collection at Tubingen is very fine, and his descriptions and figures 

 indicate a full representation of species, though Collenoti is not present. 



Chapuis and Dewalque show that the Luxemburg rocks contain several differ- 

 ent forms of the genus, though they are not so numerous as in South Germany 

 or England. Schlonbach shows that there is an obtusus horizon in North Ger- 

 many containing the usual forms, but only fossiliferous in certain localities, and 

 Brauns publishes similar results in his work. This horizon according to Schliiter 

 does not appear to have been represented in the Teutoburger Walcl, unless his 

 Gmuendense bed and the broken beds mentioned on page 48 of his work be con- 

 sidered the equivalent of all the beds between the Angulatus and Earicostatus 

 horizons. 



The English fauna, according to Wright's " Lias Ammonites " and the collec- 

 tions examined by me, has all the principal forms, and often very large shells, 

 and there are also, as in the CSte d'Or and Rhone basins, representatives of the 

 extreme modification of this genus, Ast. Collenoti. 



This series had, therefore, a more general development in all the basins we 

 have considered than any of the preceding series, but in spite of this there seems 

 to be a preponderance of forms in favor of England and France. The unusual 

 case of an early appearance of the radical species Ast. obtusum in the Luxem- 

 burg region should have its due weight, but the evidence of an equally early 

 occurrence in the South German basin shows that Ast. obtusion probably made 

 its appearance as an autochthone upon the level of the Upper Bucklandi bed in 

 the South German basin, and was thence distributed. It is probable that the 

 series subsequently met with more favorable conditions in the Cote d'Or and in 

 England than in any other basin. 



OxYNOTICERAS. 



Oxynoticeras oxynotum, the radical species of its peculiar series, appeared in 

 such profusion and with such excessively compressed and involute whorls in 

 the Northeastern Alps, South Germany, the Cote d'Or, and England, that one 

 seems to be dealing with contemporary migrants from some unknown fauna. 

 With regard to this conclusion, however, it may be well to be cautious. The 

 morphological gap is not so great as appears between an adult of a species like 

 Oxyn. oxynotum, and Agas. striaries or Icevigatum. This is indicated clearly by the 

 development of the individual in Ast. obtusum, oxynotum, and Agas. Scipionianum, 

 as we have tried to show in the previous pages and in the descriptions of the 

 genera and species. 1 Oxyn. oxynotum was a species with a highly accelerated 

 development, and in such forms the departure from allied forms took place sud- 

 denly. In consequence of this abbreviated mode of evolution gaps were left in 

 the series which it is difficult to fill. The evidence with regard to the connec- 

 tion of Ast. Collenoti with Ast. obtusum and the young forms of Oxyn. oxynotum, 



1 See young of Oxyn. oxynotum, pi. x. fig. 4, 5, and 14-17, and Summ. PI. xiii. fig. 9, 10, and compare 

 with Agas. Icevigatum, pi. viii. fig. 9, 10, and striaries, pi. ix. fig. 14, 15. 



