part 4] JURASSIC cheoxologt : lias. 307 



and others with the forms to which Quensteclt has given names — 

 M. nodosissinnim,^ 21. enode,^ 21. gicjas.^ In this set catagenesis 

 to smooth occm's without an inflated stage and without much 

 umbilical contraction. 



2. The iiiJJafum set: — This starts from 21. dejyressum, an 

 offshoot of the hirclii set while in its prime, and it continues 

 anagenesis until a maximum whorl-inflation of about 50 per cent, is 

 reached, after which decline sets in. Between 2L. depressuui with 

 32 per cent, of inflation and 21. inflafum with 50 there is eviden tly 

 room for another species : 21. sepiixjerum comes here, but does not 

 quite satisfy as a link, because of its more distant ornament. 



3. The heherti series : — This branches off from 21. depreisum, 

 perhaps, or some morphic equivalent ; but it is a series much later 

 in date. It goes through an inflated, period similar to the last, 

 running up to 42 per cent. Then it rapidl}'- declines, broadens and 

 compresses the whorl, becomes smooth, and presumably ends off in 

 a smooth subplatycone series — such as Ammonites roherti Hauer,^ 

 Reynes,^ A. lorioJi Hug,^ A. steinmanni HugJ A. phimariiis 

 Dumortier.'^ Specimens Avith the catagenetic characters of those 

 just named are in Mr. Tutcher's cabinet from about leckenhiji of 

 Radstock : they have a bituberculate Microderoceratan stage in 

 inner whorls and a Microderoceratan suture-line. 



4. The Deroceras stock : — This would branch like the last from 

 sume morphic equivalent of 21. depressum, an early stage being- 

 represented by JDeroceras hispinigeriim. This line does not go 

 through an inflated stage while bituberculate, but it loses this 

 character early, dropping the inner row of spines, compensating by 

 enlarging the outer row and broadening the periphery, producing 

 in some cases in the luiituberculate stage not true inflation but 

 forms broad in the venter with much divergent sides — a method 

 of producing cadicones ultimately. But there must be several 

 lineages now combined in Deroceras — and in some of them the 

 morphogeny must be complicated, with apparently, alternations of 

 anagenetic and catagenetic stages of ornament. 



(c) Geo]o<>ical Inferences from the Described Species. 



D o m e r i an. — Lepfaleoceras is interesting for its rarity. Among 

 the hundreds of British Domerian (Marlstone Series) ammonites 

 that have passed through my hands, T reuiember only the three 

 specimens now dealt with ; and I can recall but few cases of similar 

 Hildoceratids.^ Mr. Spath says that ' even in the British Museum 

 collections Mesoliassic Hildoceratids are almost unrepresented." ^^ 



^ 'Ammoniten d. Schwabischen Jura' x\-iii, 7, Am. hirchi nodosissimus. 

 - Ibid, xviii, 9, Am. InrcJii enodis. 



■^ Ibid, xviii. 13, Am. hirchi gigas. ^ Loc. jam cit. 



•' ' Mon. Amm.' pi. xxx, figs. 13 & 14 (copj- of Hauer). 

 '■• Abh. Schweiz. Pal. xxvi (1899) pi. viii, fig. 1 & pi. ix, fig. 2. 

 ' Ibid. pi. ix. figs. 1 & 2. 



^'^ 'Bassin du Rhone ' vol. iii (1869) pi. xvii, figs. 1-3. 

 ' Excluding Seguenziceras. ^'^ Op. jam cit. p. 547. 



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