452 ME. 8. S. BUCKMAJSr ON THE GROTJPING OF SOME [Aug.1898, 



stock makes its appearance before another genus showing less 

 removal therefrom. Or, put in another way, a genus showing a 

 mature stage with greater dissimilarity to its young stage occurs 

 before a genus showing a mature stage with less dissimilarity, which 

 is equivalent to saying that the more phylogenetically-developed 

 genus occurs before the less phylogenetically-developed genus. ^ 



Instances may be given : — Amaltheus before PaltoiAeuroceras^ 

 Dactylioceras before Stepheoceras^ and Stejoheoceras before Cosloceras 

 Blagdeni, as also the case of Strigoceras and Strigoceratoids men- 

 tioned later (p. 460, 3rd footnote). 



In other cases a later genus is more developed in some respects 

 and less in others than a preceding allied genus, showing that the 

 preceding genus is scarcely the exact ancestor of the succeeding 

 one, for instance Ludwigia and Graphoceras. A similar principle 

 is noticeable among the genera of Hildoceratidse as a whole — the 

 earlier genera are sometimes more developed in some respects than 

 the later. This is probably very much the case with the successive 

 series which have been marked in Table II as Oppeloids. They 

 are, possibly, often successive offshoots from less modified forms, 

 not descendants from one another. Therefore I have not joined 

 them in the table. The same may hold good with other stocks, 

 even to a greater extent than I have indicated. 



V. Notes ois certain Gteneeic Names. 



In connexion with the Table of ammonite-genealogy the oppor- 

 tunity is taken to propose certain new generic names, to emend 

 others which require modification, and to make certain remarks 

 concerning particular appellations. 



Genus Aetetites, Waagen, emend. 

 [Type : Arietites Tumeric J. de C. Sow.] 



This is merely a matter of arrangement. "Waa gen's Arietites 

 was practically preoccupied by Hyatt's genera Aste7-oceras, Arnio- 

 ceras, etc., and is therefore inapplicable to any of the species which 

 belong to them. However, Turneri does not seem to tall into that 

 categor5\ Certainly it has been placed in Asteroceras, but that is 

 partly because its specific identification has been so often incorrect. 

 It is really quite distinguishable from Asteroceras on account of the 

 mode of ribbing, especialh" the long forward projection of the 

 costse on the peripheral area. 



Instead of proposing a new generic name, it seems feasible to 

 use Arietites in a definitely restricted sense — applicable to a species 

 which was not generically appropriated at the time when the name 

 was proposed. Then Turneri becomes the type in this sense. 



^ Awant of exact technical terms is felt hei'e. More phylogenetically- 

 deTcloped may denote a series which is retrogressive, or \^hich exhibits what 

 are technically called phyl-hjpostrophic characters in the race — hypostrophic 

 in the individual. See ' Human Evolution,' Nat. Sci. voL x (1897) p. 188. 



