1899.] OSTBOLOGY OF THE PYG0P01>ES. 1041 



The form of the patella and cnemial process of the Alcidae more 

 nearly resembles that of the Impennes, as does, to a lesser extent, 

 the pelvis. 



The form of the tarso-metatarsus in the Grebes and Divers is 

 very similar. That of the Grebe may be distinguished froai the 

 Diver by tbe larger size of the intercotyJar tubercle and the great 

 depth of the inner glenoid surface for the inner tibio-tarsal condvle. 

 In both groups the tarso-metatarsus is much compressed laterally, 

 and the ectotrochlea is much reduced. The hypotarsus is simple. 

 Other characters will be found in the Key (p. 1044). 



The phalanges of the toes are much dattened dorso-ventrally, 

 the ungual phalanx especially so. The 4th digit is longer than 

 the 3rd. 



X. Summary. 



The present paper affords good e\idence in favour of the views 

 of Beddard, Fiirbringer, Gadow, and others who hold that the 

 Grebes and Divers are closely related, but refuse to associate 

 them with the Auks and Gulls as was done by Huxley and 

 others. 



The Pygopodes (^the Colymbi of Beddard) seem to be nearly 

 related to the Tubinares, the Impennes, and the Steganopodes ; 

 but, as Mr. Beddard remarks, " any comparisons bristle with 

 ditliculties."' 



That Hesperornis rightly belongs to this sub-order there can no 

 longer be any doubt, after Prof. D'Arcy Thompson's admirable 

 memoir ; there is one point which has apparently escaped the 

 notice of this writer, however, with regard to the pelvic girdle of 

 Hesjjerornis. This differs from that of both Grebe and Diver, 

 in that the pre- and postacetabular ilium form one great, vertical 

 and laterally compressed blade of very considerable depth. In the 

 Grebe and Diver the preacetabular ilium takes the form of a 

 narrow blade, twisted so as to lie in an obliquely horizontal position. 

 Furthermore, Hesperornis seems to be peculiar in that the in- 

 nominate bones meet throughout in the mid-dorsal line, above the 

 neural crest of the synsacrum ; in this particular, however, it 

 approaches the Grebes, where the postacetabular ilium behaves in 

 this way ; similarly it agrees with the Grebes in the shortening of 

 the sternum and the large size of the patella. These last two 

 points, however, must be regarded as coincidences rather than 

 indications of aifinity ; that is to say, Hesperornis must not on 

 account of these points be regarded as more closely allied to the 

 Grebes than to the Divers. Indeed, its sternum differs materially 

 from that of both these families in that it was keelless, whilst the 

 patella differs from that of the Grebe in being pierced by a fora- 

 men for the ambiens. But these and other points will be found 

 exhaustively discussed in the memoirs of Marsh and D'Arcy 

 Thompson. 



Mr. Beddard regards the Grebes and Divers as representing two 



