248 IIAMITES. 



priately placed here, tlie chanicteis of which, aside from the 

 mode of curvature, ally it to Hamites^ the slight distortion of 

 the shell not justifying an independent genus. That an indepen- 

 dent genus cannot be established for these forms, is certain, and 

 doubt only exists as to whether they should be referred to 

 Hamites or Turrilites, a question which can only be definitely de- 

 cided when the shells are more accurately and completely known. 



With the change in the spiral, a change often takes place in 

 the sculpture, which is often distinctly strengthened ; this is 

 however, not the case with the commencement of the series of 

 forms, but occurs somewhat later, some time after the sepai'ation 

 from the involute ancestral form. 



A character which appears with remarkable constancy in the 

 involute Lytoceratidse is gradually lost in their evolute success- 

 ors, namely, the two-pointed ending of the antisiphonal lobe. 

 In some of these this part is retained, as is shown in part 

 by existing figures, and partlj'^ as I have learned from a study of 

 the Pictet Collection, this is the case in Grioceras depressum^ 

 Ancyloceras alternatum, satissureanum, pseudoelegans, Hamites 

 boiichardiamus, altemo-tuherculatus^ elegans. In many others, 

 however, a one-pointed structure steps in, and I could convince 

 myself that this occurred by one point uniting with the other : 

 it is very apparent in forms which are derived from the spiral 

 in one plane that a distortion takes place, although a one-pointed 

 antisiphonal appears also in forms in which the spiral is in one 

 plane, even though from the minuteness of this character I could 

 not unqualifiedly admit this in respect to all the species which 

 are figured in this manner. 



For the forms here named one genus is quite sufficient, and 

 we choose, for evident reasons, the oldest name, Hamites. Rela- 

 tive to the other cretaceous Ammonites, compare below on 

 Turrilites, Baculites, Scaphites and Grioceras. 



In the lowest cretaceous strata (Berrias) we find no Hamites., 

 and in general no evolute Ammonites ; the oldest representative 

 may be considered to be H. Yvanii, from the appearance of which 

 the genus extends through the whole cretaceous ; the3^ seem to 

 reach their maximum of development in the gault. 



Hamites is certainly not a monophyletic genus ; whilst the 

 majority of the forms stand in closest relationship to Hamites 



