L. F. Spath — Notes, on Ammonites. 67 



auxiliaries may be found, shows the unimportance of this character 

 for classificatory purposes, even if, occasionally, it be constant in a 

 group of forms. 



Workers on Ammonites recognize that the details of the suture- 

 line may vary greatly in a given species. Noetling, 1 e.g., in his 

 research on the suture-line of Pseudosageceras multilolatwm, examined 

 many specimens, but found no two suture-lines alike. On pi. xxvii, 

 e.g., he figures forty-eight suture-lines, arranged in six groups, 

 and showing a great variability both in the ventral and in the 

 first lateral lobes. Pompeckj • thinks that Oxynoticeras oxynotum 

 presents as many varieties. On the other hand, the writer 3 found 

 that the suture-line of young specimens of Tragophylloceras Loscombi 

 was very constant, and that the only variability noticed was in 

 relation to the degree of complication at a given size ; whereas in 

 larger examples, again, no two suture-lines were exactly alike. This 

 only confirms that the development of the suture-line should be 

 studied, from its first, angustisellate beginning, and when this, in 

 conjunction with the development of all the other features of the 

 shell, is used as a basis for classification, variability within a species 

 will prove no obstacle. 



That in Phylloceratidae and Lytoceratidaa neither this variability 

 and obliquity, nor the features of instability already referred to, 

 are apparent, seems to the writer of some significance. 



Spacing of the Septa. 



Hyatt stated 4 that the septa " vary exceedingly in number among 

 different species and also at different ages of the same individual, but 

 they are tolerably constant, as a rule, within the limits of one and the 

 same species, if specimens of the same age are compared. They 

 follow one another in regular succession, but, as observed by Hyatt, 

 the intervals are relatively greater in the young, more constant in 

 the adult, and then markedly decrease in the oldest stage of 

 development". Bather, before Hyatt, had been more definite, and 

 stated that the " radio of the normal septal intervals was constant in 

 any given shell, while the approximation of the last septa was 

 a geratologous character". 5 Blake 6 remarked with regard to the 

 latter statement that "if any law could be founded on this and 

 applied to phylogeny, we should not find the ratio of the second 

 chamber to the first so variable as Barrande has shown it to be, nor 

 should we find approximate septa in the early Orthocerata, nor 

 crowded sutures in Ammonites at their acme". 



Both in Nautili and in Ammonoids there are many irregularities 

 in the spacing of the septa. Mr. Crick 7 mentioned "two Nautili 



1 PalcEontographica, vol. li, pts. v, vi, p. 259, 1905. 



2 "Notes sur les Oxynoticeras clu Sinemur. Super, du Portugal, etc.": 

 Comm. Serv. Geol. Portug., vol. vi, pt. ii, p. 219, 1906. 



3 Op. cit., 1914, p. 346. 4 Op. cit., i, p. 510, 1900. 



5 "The Growth of the Cephalopod Shells": Geol. Mag., Dec. Ill, 

 Vol. IV, pp. 446-9, October, 1887; and " Shell -growth in Cephalopoda 

 (Siphonopoda) " : Ann. Mag. Nat. Hist., ser. VI, vol. i, pp. 298-310, April, 

 1888. 



6 " The Evolution and Classification of the Cephalopoda, an Account of 

 Recent Advances " : Proc. Geol. Assoc, vol. xii, p. 291, 1892. 



7 Proc. Geol. Soc, No. 979, p. 3, November 11, 1915. 



