L. F. Spoilt — Notes on Ammonites. 173 



inhabitants its own peculiar stamp ; but when an Ammonite is 

 described as, e.g., Phylloceras m edit err aneum (Neumayr) race indica, 

 Lemoine,or as Protogrammoceras cornacaldense (Tausch)var . zeugitanum, 

 Spath, it is not certain that it really represents a horizontal variant 

 or race, and not a vertical mutation. In fact, these terms can rarely 

 be safelv employed, and an attempt to trace the mutations of, e.g., 

 Quenstedtoceras through E,. Douville's beds H x to H 6 shows the 

 unsatisfactory and difficult nature of their use. i5ut on the 

 examination of many hundreds of specimens of a variable species such 

 as Hystrichoceras varians (Sowerby), Cardioceras cordatum (Sowerby), 

 or Xipheroceras planicosta (Sowerby) (out of one block or bed, and, 

 therefore, apparently contemporaneous) and as an alternative to 

 using the term "variety" or creating new names, the use of the 

 trinomial nomenclature suggests itself for these thick and thin, 

 involute or evolute, weakly or strongly ornamented variations, as 

 employed by, e.g., Solger for Eoplitoides ingens nodifer, H. ingens 

 costatus, and H. ingens Icevis. Wepfer 1 also reintroduces Quenstedt's 

 trinomial nomenclature, but in a different sense. The genetic 

 relationship between the Bajocian subradiata-gvou-p and theTithonian 

 lingulati is too uncertain to include them all in the genus Oppelia, 

 and, moreover, even such names as GlocJiiceras lingulatus carschtheis, 

 61. lingulatus Icevis, and Gl. lingulatus crenosus, covering forms from 

 different facies and different horizons between the bimammatum zone 

 and the Tithonian, would not be admissible. 



What has been said with regard to the form and coiling applies 

 also to the use of the ornamentation of the shell for classificatory 

 purposes. Von Buch's sections with a keeled or grooved venter, or 

 Mojsisovics's divisions of Liostraca and Trachyostraca, were soon 

 found to be unnatural groupings. " Aegoceras" sagittarium, Blake, is 

 an Asteroceras, though it has no keel ; " Oxynoticeras" Greenotighi 

 (Sowerby) is a Schlotheimia though it has no ventral groove. An 

 Argovian Nenmayriceras, e.g., may have a groove on the ventral region 

 of the chambered portion which, generally with the beginning of the 

 body-chamber, changes into a keel. This passes into an interrupted 

 line of tubercles which, disappearing abruptly, may again give way 

 to a groove. According to whether this groove or the dentation 

 is more pronounced, there are several combinations; at the same 

 time the sides are often conspicuously smooth and the body-chamber 

 often becomes abnormal and depressed. 2 And all this in one and the 

 same form. Again, the presence of a hollow carina, though 

 occasionally constant, and the thickness of the siphuncle — at one 

 time considered a distinction between " Harpoceras " and Oppelids — 

 cannot be used for classificatory purposes. 



Mojsisovics had at first 3 considered all post-Triassic Ammonites, 

 except Phylloceras and Lytoceras, to be descendants of the 



1 "Die Gattung Oppelia im siiddeutschen Jura": Palasontographica, 

 vol. lix, pp. 1-68, 1912. 



a Wepfer, op. cit. , p. 17. 



3 "Die Cephalop. d. Mediterr. Triasprovinz " : Abh. k.k. Reicksanst., 

 vol. x, 1882. 



