548 me. l. r. spaxh on [Dec. 1913, 



•desirable to propose a more detailed classification of these forms, 

 when one has to rely largely on the published descriptions of 

 previous authors. I will indicate, therefore, only a few groups into 

 which the ammonites in question might be collected within the 

 genera Segnenziceras Levi ( = Arieticeras Seguenza) and Protogram- 

 moceras, nov. Further subdivision will doubtless be necessary as 

 our knowledge of these forms grows. 



The classification is based on the course of the radial line, in the 

 first place, as the most constant feature of the shells. Mr. S. S. 

 Buckman has shown how it may well be used, in conjunction with 

 the suture-line, as a basis for classification 1 in the Hildoceratidse 

 in any case. Objections on account of the change in the radial line 

 on the same ammonite will hardly be raised. Such changes do 

 occur, not only in Hildoceratidse (notably, for example, in certain 

 Ludivigellce), but also in many other families (' Polymorphidse ' : 

 Fontannesia ; Oppelidse : ' Haploceras,' etc.). They are always 

 limited to, at most, the last 30° in circular measure of the 

 body-chamber, leading up to the mouth-border, and can easily 

 be distinguished. By far the greater part of the body-chamber 

 and the previous whorls have, for all practical purposes, an identical 

 radial curve. It is interesting to note here that, even in cases 

 where the irregular development of the ornament is said to be 

 very striking, as in Indoceras baluchistanense Ncetling,- the sig- 

 moidal course of the radial line is really fixed, and it seems that 

 only the change in its character (from striate to costate) follows no 

 law. 



With regard to the suture-line, I am fully aware of the difficulties 

 attending the proposed classification. The sutures of these early 

 forms are too similar in general outline to have received much 

 attention in the past, and they are, therefore, but imperfectly 

 known. We now know, however, that in some striking cases an 

 identical radial line may be combined with a notable difference in 

 the suture-line, and I am quite unable to endorse Dr. Bosenberg's 

 view. That author, 3 after studying well-preserved material, refrained 

 from giving detailed descriptions and figures of the sutures of his 

 * Harpocerates ' because ' they offer no or only very slight dis- 

 tinctions for specific separation.' In fact, a comparison of the 

 sutures given by Dr. Fucini i for his various forms of ' Harpoceras,' 

 ' Grammoceras,' and ' Hildoceras' seems to show that they differ 

 more in ' species ' of the same genus than they do in certain 

 ■* species ' of different genera. But this merely emphasizes the 

 undesirability of adopting Fucini's classification. He deems it 

 impossible to separate the varieties costicillatum and inseparabile of 



1 ' Inferior Oolite Ammonites : pfc. 10 — Supplement ' Monogr. Pal. Soo. 

 vol. lii (1898) pp. i & ii. 



2 F. Needing, ' Die Entwicklung von Indoceras baluchistanense Noetlg.' 

 Geol. & Palseontol. Abhandl. (Jena) n. s. vol. viii (1906) pt. 1. 



3 ' Liasische Cephal.-Fauna der Kratzalpe ' 1909, p. 288. 



4 'Ammoniti del Lias Medio dell' Appennino Centrale' Pal. Ital. vol. vi 

 (1900-1901) pp. 17-65 & test-figs. 24-48. 



