1923 SYSTEMATIC 55 



Kellaways Cla3% 3, 4, (and 7, see remark below), Kellaways Rock, i, 

 Callovian (foreign), 6, 7. It may be taken as certain that genera 

 3 and 4 are later than 2, 5. It may be assumed that the other genera 

 are as late or later than those of the Kellaways Clay ; but the exact 

 chronology is not proved. 



From the external hkeness of DolikepJuilites to Tmetokephalites, 

 the argument might be put forward that the difference in suture-line 

 is sexual — the former vdXh. its simple suture-Une being the male, and the 

 latter with its elaborate one being the female. And as both were said 

 originally to come from the same stratum and locaUt3% Combrash, 

 Peterborough, the suggestion seems to have force. But examination 

 of the matrix of Tmetokephalites shows that it is not an English specimen. 

 Comparison with Wurtemberg examples makes it fairly certain that the 

 specimen is from there, from Oeschingen. So the sexual idea breaks 

 down — ^where other sexual readings of Ammonites have failed — that 

 the stratum or the locality, or both, are different : it is absolutely 

 necessary that the indixiduals supposed to be two sexes of one species 

 be syntopites : they must have Uved in the same place at the same time. 



Since this was ^\Titten, an English example of Tmetokephalites has 

 been seen — in an old collection lately acquired by Mr. Tutcher. It is 

 from the Kellaways Clay of Wiltshire. 



The likeness of these two genera shows the importance of ascertaining 

 the suture-Hne. The identification of Ammonites is not difficult in 

 itself ; it is only hard in that it demands time, obser\'ation and patience. 

 At present, the suture-line can seldom be safely neglected. In the 

 future, when the association of certain external features \\\\h certain 

 suture-hnes has been fully illustrated, it should be possible to predict 

 what suture-hne is associated with given external features ; for it ma\- 

 be taken as certain that there are such differences — in the case of these 

 two genera rather more rib-flexure in Dolikephalites than in Ttneto- 

 kephalites. But until these associations of features are knoN\Ti and 

 proved by many more examples, the first necessity in the identification 

 of Ammonites is to obtain the suture-Une, often a laborious task. 



The following rectifications of genotA^'pes are necessan,'. They are 

 due to the rule that the first output of a new generic name, definitelv 

 hnked \\'ith a trivial name or names, makes the form or forms so cited 

 the genoholotj'pe or genos}-nt}^es, as the case ma}- be, although such 

 was not the author's intention at the time of proposal. Certain generic 

 names which were given in the foUowng works take genot\-pes different 

 from what were subsequently stated ia my " Monograph of Inferior 

 OoUte Ammonites " — in some cases the result is particularly unfortunate ; 

 but there is good reason for the rule, although the author was not aware 

 of the rule at the time. 



In Mon. I.O. Amm., Sup., in consequence of plates and explanations 

 being issued in advance of text, the foUovving genotj-pes take precedence : 



Pleydellia, S. B. p. comata S. B. (Suppl. PL x, f. 11-13) is 

 genotype, preceding P. aalensis. 



Brasilina, S. B. B. crinalis (Suppl. x, 29-31) and B. haylei 

 (Suppl. XI, 34) are genosjutypes, preceding B. tutcheri. Genolectotype 

 B. haylei. 



The following casual citations in Proc. Cotteswold Field Club, 

 XIII, 1901, p. 266, made genot^-pes : — 



Cypholioceras, S. B. " C. opaliniforme " precedes C. plicatum. 



