250 DR. A. E. TRUEMAN ON THE [vol. lxxiv> 



Hyatt's genera to express this interpretation, and limited each 

 generic name to a series which evolves from Capricorn to bituber- 

 culate sphaerocone (1, vol. i, p. Hi). That is to say, those generic 

 names which were formerly applied to morphic equivalents on 

 several lineages were made to include the heteromorphic stages of 

 phylogenetic series. JSLicroceras was applied to an earlier series, 

 while Androgynoceras and Lijparoceras were limited to series of 

 those ammonites that have respectively elevated and depressed 

 whorls. At a later date A. Hyatt 1 used the name Amhlycoceras 

 to include certain capricorns ; the specimen then figured is peculiar 

 in having costse with a slight peripheral curve, and Mr. Buckman 

 proposes to restrict the name for such a series. 2 Oistoceras was 

 suggested for capricorns in which the ribs have a very distinct 

 bend on the periphery, more marked than that shown by Amhly- 

 coceras (1, vol. i, p. iv). 



Recognizing that there exists at least another series of ammonites 

 passing through comparable stages, Mr. Buckman used Waagen's 

 name JEc/oceras 3 to indicate them, including here A. natitiliformis 

 J. Buckman, which had frequently been confused with A. bechei, 

 but from this it is separated by a very consakdjcajble'i time-interval 

 (1, vol. i, p. Hi). 



Summarizing, then, the existing classification of /these ammonites, 



we find the following genera in use : 



t 



Liparoceras — Depressed forms with coarse ornamentation. 



Genotype selected by Mr. Buckman : A. striatus Bronn, non Reinecke. 



Androgynoceras-- Elevated whorl, finer ornamentation. 



Employed to include A. maculatns Young- & Bird, A. heterogenes 

 Young- & Bird, A. bechei Sowerby, A. henleyi Sowerby, and many 

 English capricorns. 

 Genotype selected by Mr. Buckman : A. hybrida A. d'Orbigny. 



Amhlycoceras — Capricorns only hitherto described, with slight peripheral 

 rib-curve. Not otherwise defined. 



Oistoceras — A series with marked rib-curve on the venter. 



Genotype, A. jigulinus Simpson. Capricorn stage only known. 



JEgoceras — Includes capricorns believed to lead to A. natitiliformis 

 J. Buckman. 



Genotype, Ammonites planicosta (=capricomus) A. d'Orbigny. 



In constructing the above-named genera little attention has been 

 paid to any characters, except whorl-shape and ornamentation ; 

 the sutures have not been compared, and the less obvious details 

 of ontogeny have not been examined. Thus the characters hitherto 

 described are not sufficient to identify a single genus with any 

 certainty ; indeed, the species referred to certain genera are in no 



1 In Eastman-Zittel, ' Text-book of Palaeontology ' 1st ed. vol. i (1900) 

 p. 578. 



2 S. S. Buckman in 'Geology of the Country , between Whitby & Scar- 

 borough ' Mem. Geol. Surv. 2nd ed. (1915) p. 95. 



3 W. Waagen, ' Die Formenreihe des Ammonites sub rod ictus' 1869, p. 247. . 



