296 



ME. S. S. BIJCKMAJs^ ON 



[vol. Ixxiii, 



For the same purpose of comparison, outline rib-schemes are 

 given in figs. 15-21, p. 295 : — 



Fig. 15. Oxynoticeras oxynotum, after Quenstedt. 



rig. 16. 0. oxynotum {Ammonites mltellus), see note to fig. 2 above. 



Fig. 17. 0. polyophyllum. after fig. in Y. T. A., see note to fig. 3 above. 



Fig. 18. Gnihaiiceras guihaliamim, after D'Orbigny. 



Fig. 19. Victoriceras victoris, after Dnmortier. 



Fig. 20. Gleviceras glevense, from the specimen figured in PI. XXVIII, fig. 2. 



Fig. 21. Radstockiceras complicatiim, from the specimen depicted in PL XXVII. 

 fig. 1 : this outline is of the natural size. 



The genotypes of these Oxynotoid genera are all in about the 

 same stage of morphic equivalence, but all differ in degree of 

 development of various characters. Thus, in regard to suture-line, 

 some make more elaboration in the lobules of the external saddle, 

 some in the superior lateral lobe; in regard to periphery, Oxijno- 

 ticeras is the only one that has attained to the knife-edge stage, 

 ^adstocMceras approaches, Gleviceras is far from it. An analysis 

 of the genera on these and other features gives the following- 

 results in descending: order : — 





Saddle. 





Sup. lat. lobe. 



Periphery. 



5. 

 4. 

 3. 

 2. 

 1. 



Radstockiceras. 



Oxynoticeras. 



Guihaliceras. 



Victoriceras. 



Gleviceras. 



5. 

 4. 

 3. 

 2. 

 1. 



Radstockiceras. 



Gleviceras. 



Victoriceras. 



Guihaliceras. 



Oxynoticeras. 



5. Oxynoticeras. 

 4. Radstockiceras. 

 3. Guihaliceras. 

 2. Victoriceras. 

 1. Gleviceras. 





Ribbing. 





Umbilicus. 



Result : Nat. Ord( 



5. 

 4. 

 3. 

 2. 

 1. 



Victoriceras. 



Oxynoticeras. 



Radstockiceras. 



Gleviceras. 



Guibaliceras. 



5. 

 4. 

 3. 



2. 

 1. 



Radstockiceras. 



Victoriceras. 



Oxynoticeras. 



Guibaliceras. 



Glevicera?. 



5. Radstockiceras (22) 

 4. Oxynoticeras (17). 

 3. Victoriceras (16). 

 2. Guibaliceras (11). 

 1. Gleviceras (9). 



The natural order is arrived at by adding the position-marks 

 attained under the five different bases of analysis. 



Amaltheus Jymensis Wright (pi. xlvi, figs. 1-3 & pi. xlvii, 

 figs. 1-3) cited as Oxynoticeras lymense in my Chronological paper, 

 p. 270, would seem not to belong to any of these genera. To be 

 Oxynoticeras it should have a suture-line more comj^licated than 

 that of O. ijolyophyllum, but its skeleton outline is more that of 

 Guihaliceras. 



Genus Aeietites Waagen. 



Aeietites tuegescexs, sp. nov. (PI. XXIX, figs. 2 a & 2h\ 

 PL XXXI, fig. 5.) 



Cf. 1864c Ammonites turneri Wright (nan J. de C. Sowerby sp.), ' Amm. of Lias ' 



Proc. Cotteswold Club, iii, pi. ii, fig. 4. 

 Cf. 1879. Arietites Uirneri Wright {nan J. de C. Sowerby sp.), 'Lias Ammonites ' 



pi. xii, figs. 1-3 ; 1881, p. 292. 

 Cf. 1879. Ammonites hrooTci Kevnes {nan J. Sowerby sp.), 'Men. Amm.' pi. xliii, 



figs. 6 & 7.' 



^ These three references happen to be all figures of one specimen ; see p. 322. 



