306 ME. s. s. BrcKMAN ON [vol. Ixxiii, 



which is not Oppel's species, for that was founded on Ammonites 

 Irevispina D'Orbigny (^non Sowerby). Its proportions are dif- 

 ferent. Dumortier's is a thicker form ; D'Orbignj^'s is a further 

 stage on in compression and degeneration : it gets back to the 

 smooth stage. 



Table XIX. — Proportions : Microderocerates. 



1. Microderoceras hircJii (Sowerby). 



(Ammoniteshirchi Sowerh J, -pi. CGh.Yiiy F. 204, 25, [26?], 57. 



i^goceras UrcU Wright, -pi. xx.ni)-... F. 160, 22, 23, 58. 



f Microderoceras depressum, nov. 



(Holotype, Barrow specimen) S. 75, 29, 32, 47. 



{Ammonites hirclii Dumortier, xli, J F. 197(94), 28, 29, 51. 



p. 130)^ It. 197, 28, 31, 50. 



2. <{ Microderoceras septigerum, nov. 

 {Ammonites hirchi J . Bnckm.a,n) / S. 42, 33, 43, 45. 



ts. 89, 35, 40, 42. 



Ti/T- 7 • ^ ^ [ S. 64, 34, 50, 45. 



Microderoceras inflatum^noY <^ ^ ,0-1 on qo a a 



f Microderoceras hisinnatum (Geyer). 



{2Egoceras hispinatum Gejer) F. 55, 30, 35, 46. 



Microderocercts rhodanicwn, noY TF. 35, 32, — , 44. 



{Ammonites heherti Dumortier). J T. 35, 31, 42, 37. 



1 F. 77, 34, — , 45. 



Lt. 74, 32, 29, 45. 



3.^ 



Microderoceras heherti (Oppel). 



{Ammonites hrevis^nna D'Orbigny, fF. 74(47), 



32, 



24 



32, 



24 



31, 



25 



45. 



Ixxix)-^ ^ F. 140(90), 32, 24, 47. 



(t.140, 31, 25, 47. 



Microderoceras roherti ' (Hauer) . 

 1^ {Ammonites rohertilLdiUQv, Hi) '" T. 97, 36, 23, 40. 



jSLicroderoceras septigerum and J\I. inflatum are species suffi- 

 cientl}^ ahke to make it probable that they indicate beds of the 

 same date. More will be said on this point present^ (p. 311). 

 Curiously enough, I have not found in literature anj'-thing really 

 like these inflated forms. The most comparable species are 

 Ailgoceras prcecursor and .^. l)is2oinatum Geyer, possibly of 

 basal Eaasayah, Deroceras hispinigerum (p. 302), low in Raasayan, 

 3ficroderoceras rJiodanicum (p. 305), presumably top of Raasayan 

 ileclteiibyi). All differ in proportions from the inflated forms, 

 as Tables XVIII & XIX show. 



The placing of certain bituberculate species to jSLicroderoceras 

 and others to Deroceras must be regarded as conventional. I am 

 not prepared at present to state the difference between them : the 

 study necessary for that might delay this Appendix for several 

 years ; and it is a biological matter. 



This, however, may perhaps be said : various branches of Micro- 

 deroceras may be noted : — 



1. The hirclii set— the A. hirchi oi Sowerby, Wright, D'Orbigny, 



^ ' Mineral Concholog-y.' - ' Monogr. Lias Ammonites.' 



■^ ' Bass. Ehone,' vol. ii. ■^ ' Pal. fran9. : Terr. Jur. Ceph.' 



'° ' Capric' Sitzungsber. k. Akad. Wissensch. Wien, vol. xiii (1854) p. 94. 



