1875.] 



369 [Hyatt. 



BUCHICERAS (nov. genus.) 



Paleontologists have been aware for many years, ever since, in 

 fact, Von Bucli published his work upon Ceratites, that the so-called 

 cretaceous Ceratites differed from the triassic forms in the charac- 

 teristics of the sutural outlines. Being obliged to describe the follow- 

 ing species I find that, as Quenstedt has already pointed out, these 

 forms are not Ceratites at all, but, strictly speaking, Airmonites. 

 They show this in the form of abdominal cell in the young, the char- 

 acteristics of the superior lateral cells, which are invariably divided, 

 as are those of all the Ammonites proper, and also in the tendency 

 of the young sutures of Buchiceras bilobatum to assume a wholly am- 

 monitic aspect. The truly ammonitic outline of the cells and lobes 

 in Buchiceras attenuatum shows how easily the outlines of the typi- 

 cal divided cells are transformed into those of a true Ammonite by 

 a few digitations, whereas the same digitations applied to the entire 

 outlines of a true Ceratite would produce only a Ceratite, not an 

 Ammonite. 



The young have an acute but gibbous whorl, which becomes trans- 

 formed into a whorl with convergent sides and a flattened abdomen 

 in Buchiceras bilobatum, B. syriaciforme , and B. attenuatum, which 

 together form a natural series also agreeing in the possession of two 

 rows of tubercles and in the amount of involution which extends to 

 the inner row of tubercles. The young of B. serrata and B. pierde- 

 nalis were not seen at a very early age but probably are similar, since 

 the adults have very nearly the form of the young of the preceding 

 series. That a similar relation exists in the development of the 

 sutures is improbable. They, as far as traced in the young of B. ser- 

 ratum, indicate a common genesis .from B. bilobatum. This, however, 

 must be considered doubtful, and it may be found that both B. ser- 

 ratum and B. pierdenalis spring from other and quite distinct forms. 

 B. attenuatum and Amm. Vibrayeanus D'Orb. appear to be closely 

 allied in form, though the sutures, as figured by D'Orbigny, are 

 like those of any other cretaceous species of this group. The ribs, 

 however, have the aspect of those of B. serratum, and it may be that 

 B. Vibrayeanum is allied with the latter which it more closely resem- 

 bles in its sutures. A very slight error in drawing would convert the 

 sutures of the latter into those of the former, but it is not possible 

 that they may be identical. B* Vibrayeanum has a sharp abdomen 



PROCEEDINGS B. S. N. H. — VOL. XVII- 24' MAY, 1875. 



