54 PROP. H. H. SWIKNEKTOK AXD MB. A. E. TBUEMAX [vol. Ixxiil, 



one case of asvmmetrv. Further, asymmetry of a similar character 

 has been observed by previous writers in a larye number of other 

 forms : — 



Ammonitea miserabilis Queustedt {Agassicera^ Hyatt). ^ 



Ammo)ntes falcaries Queustedt.^ 



Oxynoticeras heteroplenrum Neiimayr & Uhlig.^ 



Hoplites oxygonius Nemnayr k. Ulilig.- 



Engonoceras pierdenale var. commune Hyatt.'' 



Engonocenis uddeni Cragin.'* 



Oxyiioticeras guibali Hyatt ('Genesis of the Arietida; ' 1889, p. 219 & 



pi. X, fig. 28). 

 Cosmoceras jason (d'Orbigny). ' 

 Cosmoceras m. f. jason Reinecjke. C. proniae Teisseyre,"* C. 2'>ollux Reinecke, 



C. subnodatum, C.jenseni Teisseyre {op. cit. 1884, pp. 538-69). 

 Ammonites convolvtus Schl. (Fraas. op. cit. 1868, p. 111). 

 Ammonites denarius, fittoni. lyeUi Leymerie.'^ 



Ammonites coregonensis Sowerby, Waelxneroceras guidoni (Sowerby).^ 

 Ammonites suessi, A. abnormalis, von Hauer.^ 



It will be noted that the greater number of the fossils in which 

 this type of asymmetry has been observed are included in, or 

 connected with, the families Cosmoceratidse, ^goceratidse, and 

 Stephanoceratidse (according to the classification adopted by 

 J. P. Smith). 8 Thus it would at first appear that the feature is 

 of considerable systematic importance ; yet it should be remem- 

 bered that, although asymmetry is typical of certain species of 

 Hoplites, in other species of the same genus we have not observed 

 it. The presence or absence of examples of asymmetry, therefore, 

 must not be taken as conclusive evidence of relationship in the face 

 of other facts. 



An examination of the lists just given shoAvs that nearly every 

 specimen in which this type of asymmetry has been observed has 

 a rounded or flat venter. Although at least a third of the 

 specimens examined had keeled venters, not one case of as^^mmetry 

 has been detected by us among them. It would thus appear that 

 the displacement is to a large extent associated Avith the shape of 

 the whorl. Xevertheless, asymmetry may occur occasionally in 



^ F. A. Quenstedt, " Die Ammoniten des Schwabischen Jura ' Stuttgart, 

 1885, pi. xiii, figs. 15, 29. 



'^ M. Neumayr & V. Uhlig ' Ueber Ammoniten aus den Hilsbildungen Nord- 

 deutschlands.' Palaeontographica, vol. xxAai (1880-81) pp. 135, 171. 



"^ A. Hyatt, ' Pseudoceratites of the Cretaceous ' U.S. Geol. Surv. Monogr. 

 xliv (1903) pp. 159, 165. 



* A. d'Orbigny, ' Paleontologie Fran^aise : Terrains Oolitiques ou Juras- 

 siques' vol. i (1842) p. 448. 



" M. Neumayr & V. Uhlig, Palaeontographica, vol. xxvii (1880-81) pp. 219- 

 55. 



^ P. Sa\T & G. Meneghini, ' Osservazioni stratigrafiche & paleontologiche 

 concementi la Geologia della Toscana ' 1851, pp. 73-77. 



' F. R. von Hauer, ' Ueber einige unsymmetrische Ammoniten aus den 

 Hierlatzschichten ' Sitz. Math.-Naturw. Classe, K. Akad. Wissensch. Wien, 

 vol. xiii (1854) pp. 401-410. 



" Cephalopoda, in K. von Zittels ' Text-book of Paleontology ' (transl. 

 Eastman), 2nd ed. (1913) p. 150. 



