part 4] ETOLTJTIOX OF THE LIPAROCERATID M. 261 



Axdrogtxoceras Hyatt, 1867. 



Genolectotype : Ammonites hybrida A. d'Orbigny (3, pi xxxv, figs. 1-3, 

 non 4-5). . 



Develops from Capricorn to bituberculate spha^rocone. Whorl height 

 usually about equal to whorl thickness. Ornamentation never so 

 coarse as in some species of Liparoceras, and not usually so fine as in 

 Becheiceras. 



Suture : EL and IL about equal in depth, IL with lobules usually asym- 

 metrical, very narrow, and ES very wide (fig. 1 c, p. 258). Body- 

 chamber about three-quarters of a whorl. 



Species included l : — 



A. maculabum (Young & Bird), A. obtusicosta, sp. nov., A. hybrida 

 (d'Orbigny), ..4. divaricosta, sp. nov. 



Horizon: Davcei zone, extending from the latsecosta sub-zone to the 

 dsedalicosta sub-zone. 



In the development of Androgynoceras the outer tubercles 

 appear first ; A. lienleyl Keynes, in which the inner tubercles are 

 much more prominent than the outer, probably belongs to a 

 different series. Involution proceeds slowly, and no specimen has 

 vet been examined in which the outer tubercles are twice as 

 numerous as the inner. 



The more involute forms of this lineage have hitherto been found 

 only at Lincoln (7, p. 104). 



JEgoceras Waagen, 1869. 



Genolectotype : Ammonites planicosta A. d'Orbigny. 



Develops from Capricorn to bituberculate spha3rocone. Whorl height 

 usually about equal to whorl thickness. Ornamentation moderately 

 fine, usually a little coarser than that of Androgynoceras. 



Suture : EL and IL about equal in depth ; IL usually small, and ter- 

 minated by three fairly -symmetrical lobules ; the median lobule fre- 

 quently short ; ES very wide (fig. 1 d, p. 258). Body-chamber nearly 

 a whorl in length. 



Species included: — 



A. sequicosta, sp. nov., A. latsecosta (Sowerby), ? A. henleyi (Sowerby), 

 A. dsedalicosta, sp. nov. 



Horizon : Davoei zone, extending from the latsecosta sub-zone to tha 

 dsedalicosta sub-zone. 



The ammonites of this series are not very different from those 

 •of the Androgynoceras series ; generally the first lateral lobe in 

 JEgoceras is smaller and more symmetrical than in Androgyno- 

 ceras. The spha?rocones are also distinct, but the separation of 

 these series is not easy. 



The young, before ribs are developed on the periphery, are 

 scarcely distinguished from similar stages in the Amblycoceras 

 and Oistoceras series. Thus ribs appear at approximately the 

 same diameter, and sutural development at first proceeds similarly 

 in each group. It seems, therefore, probable that those four 

 genera had a common origin, and are much more closely related 

 than any other Liparoceratid genera dealt with in this paper. (See 

 Table III, p. 286.) 



1 Several earlier species (A. integricostatum, A. siphunculare) are also 



referred to this genus (see p. 290), but it is probable that the genera Mgoceras 

 •and Androgynoceras had not at that time become separated. 



