part 4] 



EVOLUTION OF THE LIPAROCERATID.E. 



293 



as Mr. Buckman suggested, to the Liparoceratidae (1, vol. ii, 

 p. vii). 



That is to say, two main groups of ammonites may be recognized 

 in the families mentioned : — 



(1) Those which evolved directly from a globose ancestor (Liparocera- 



tidae, Hildoceratidae, Poly mor phi dae, Echioceratidae, Deroceratidae). 



(2) Those Avhich have passed through an intermediate cadicone stage 



(Amaltheidae, Dactyloidse). (See Table IV, below.) 1 



Table IV. — Ditty ram showing the possible relationships of 

 the chief ' Liassie families of Ammonites. 



Frechiella 



Hildoceratidae 



Cymbites 



OeroceratidaE 



Amaltheida 



Cymbit 



Dactyloidae 



Polymcrphidae 



Liparoceratidae 



Echioceratidae 



Cadicone stage 



It is interesting to note that a carinate venter is acquired inde- 

 pendently in several families of each of these groups, typically in 

 the Hildoceratidae and Amaltheidae, less prominently in the Echio- 

 ceratidae and the Polymorphidse and in some members of the 

 Deroceratida?. The development of a carina is a normal progressive 

 feature ; and, while it leads to a certain similarity between some 

 forms, it does not necessarily imply any close relationship. 



VIII. References to Literature. 



1. S. S. BUCKMAN, 'Yorkshire Type Ammonites' vol. i, 1909-1912: vol. ii, 



1913-1914. 



2. A. Hyatt, ' Fossil Cephalopods of the Museum of Comparative Zoology ' Bull. 



Mus. Comp. Zool. Harv. vol. i, 1867. 



3. A. d'Orbignt, ' Pal&nitologie francaise : Terrain jurassique — I. C6phalopod.es. 



1842-51. 



4. F. A. Que>stedt. ' Die Ammoniten der Schwabischen Jura: Der Schwarze 



Jura (Lias) ' vol. i, 1883-1885. 



5. J. C. M. Reinecke, ' Maris protogtei, &c.' 1818. 



6. F. Keyxes, " Monographic des Ammonites ' 1879. (Text incomplete.) 



7. A. E. Tei'EMAS, 'The Lias of South Lincolnshire' Geol. Mag. dec. 6, vol. v, 



pp. 64-73, 101-111, 1918. 



8. T. Wright, 'Monograph of the Lias Ammonites of tho British Islands' 



Palseontographical Society, 1878-1886. 



1 It does not necessarily follow, however, that the cadicone form of whorl 

 has not been developed in groups that are unrelated. 



