48(i Mr. P. K. Lowe on the Si</iiincance of certain [Ibis, 



two pairs o£ <^roups or genera whoso differences iufe7- se I have 

 attempted to sketch we have depicted the early and late 

 phases of a species, or a group of species, as evolved in time 

 as opposed to space. Iu other words, the Grey Plover group 

 and the Kentish Plover group respectively belong to an 

 earlier geologic horizon than the Golden Plover or the 

 Common Ringed Plover group. In each of the four groups 

 we have "varieties," subspecies, or species which may be 

 regarded as more superficial present-day variations in rela- 

 tion to space ; while on the other hand in each of the four 

 groups we may observe deeper-seated structural characters 

 which represent variations or mutations in relation to time. 



Without, I venture to think, too great a strain on the 

 imagination, these mutations in time, although not exactly 

 comparable to the mutation of Waagcn *, are suggestively 

 similar ; whih' the Grey and Golden Plover groups taken 

 as a wdiolo, or the Kentish Plover and Ringed Plover 

 groups siniiliirly regarded, may be compared in some sort 

 to the phylum of modern Pahxu)ntology. 



It is at least suooestive that in what I have termed in the 

 case of either group "the early phase " we find osteological 

 characters which are more generalised, or at any rate less 

 specialised, than is the case in the hiter phase. It is obvious, 

 for instance, that the six genei'alised Pluvialine forms 

 figured under the title of Pre-Charadriine (p. 480) have a 

 remarkable morphological likeness to Tringine or Larinef 

 forms ; while those figured as examples of the Charadriiuse 

 would appear to be more specialised and more recent 

 Pluvialine forms. Moreover, as I have previously noted 

 above, in the colour-pattern characteristic of the species of 

 all the Kentish Plover group (Plate VI. figs. 1-3) we seem 

 to have an adumbration, or what may be (possibly somewhat 



* Waagen, W. " Die Formenieilie des ADimonites subradiatus." 

 Geognostisch-Palaeontologiscli Beitragc, Band ii. Heft ii. Nov. 1869, 

 pp. 179-250. For a translation of liis principles, cf. H. F. Osborn, 

 " Origin of Single Characters as observed iu Fossil and Living Aninnils 

 and Plants," Anier. Nat. vol. xlix. No. 580, April 1915, p. 2i23. 



t For a figure of tie skull of Leans canus see lljis, 191G, p. 326. 



