l2G0 DR. A. E. TRUEMAK ON THE [vol. lxxiv, 



Suture : EL and IL about equal in depth, wider than ES, IL generally 



trifid (fig. 1 a). 

 Species included : — 



L. sparsicosta, sp. nov., L. heterogenes (Young & Bird), L. obtusinodum, 

 sp. nov., L. zieteni (Quenstedt), L. heptangidare (Young & Bird), 

 L. cheltiense (Murchison). 

 L. tiara, sp. nov. 

 L. pseudostriatum, sp. nov. 

 ^Geological horizon: Upper part of the ibex zone. 



The ammonites comprising the genus Liparoceras range from 

 stout capricorns to moderately involute thick- whorled forms with 

 generally coarse bituberculation. The best-known English ammo- 

 nite belonging to this series has been called Liparoceras striatum ; 

 Reinecke's figure of this species, however, shows an involute 

 -depressed Liparoceratid with paired tubercles on the outer whorl 

 (5, pi. viii, figs. 65 & 66). Involute Liparoceratan forms from the 

 JBritish Lias have the tubercles unpaired, the outer being nearly 

 twice as numerous as the inner. It is probable, therefore, that 

 L. striatum (Reinecke) does not occur in this country, and it may 

 be a representative of another lineage, probably allied to A. striatus 

 parinodus Quenstedt (4, pi. xxix) ; L. pseudostriatum is here pro- 

 posed for some of the English ammonites which have been called 

 L. striatum. The similar fossils from Gloucestershire are members 

 jof the same genus, and include a number of forms closely allied to 

 L. cheltiense. 



The capricorns from which these ammonites arose have not 



hitherto been noticed, but are here described as L. sparsicosta 



(PI. XXI, fig. 2), while L. heterogenes is a later stage (biologically, 



at least) in the same series, having fine paired tubercles on the 



-outer whorl. 



A number of intermediate forms unite this with ammonites 

 resembling L. obtusinodum, which has fine paired tubercles on 

 the inner whorls, but develops coarse unpaired tubercles on the 

 outer whorl. A further stage is shown by L. cheltiense, in which 

 the earliest tubercles are fine and unpaired, later becoming stronger, 

 and finally transversely elongated on the last whorl, the commence- 

 ment of catagenesis being indicated by a tendency to return to 

 paired tubercles. More advanced ammonites of this lineage have 

 .finer tubercles on the outer whorl. Liparoceras heptanqulare is 

 ^probably a related species, which may be connected with L. ziefen i, 

 since both these species have a peripheral arch more pronounced 

 than is usual in the genus. 



Several other series of Liparoceratan ammonites may be distin- 

 guished, although the material available for their study is insuffi- 

 ■ cient for the establishment of lineages — one such series comprises 

 ..ammonites that develop fine ornamentation only (L. pseudo- 

 striatum). The above forms usually become comparatively in- 

 volute, but at least one series retained a moderately e volute form 

 with coarse unpaired tubercles. This series includes L. tiara 

 V (P1. XXI, fig. 1), which, notwithstanding its wide umbilicus, has a 

 -very complicated suture with deeply undercut saddles (fig. 4 d, 

 p. 270), suggesting that it is at least as advanced as L. cheHiense. 



