Skull of an Embryo Chionarchus. 315 



facets were found seated ou the processes from the ptery- 

 goids. Both processes from the basisphenoidal rostrum 

 were in contact with the facets on the pterygoids, and in 

 every respect these basipterygoid articulations seemed to be 

 as perfect and complete as in any adult Plover (such as the 

 Golden Plover), in which these articulations persist through- 

 out maturity. It may here be noted that in the Oyster- 

 catchers these basipterygoid articulations persist throughout 

 adult life; and this fact, along with others, seems to point 

 to the conclusion that, although the Oyster-catchers are in 

 some respects highly specialised, they are not so fundament- 

 ally specialised away from the true Plovers (Charadriidse) 

 as some of the more aberrant Plovers, such as the Sheath- 

 bills, Crab-Plovers, Pratincoles, Skuas, Gulls, and Terns. 

 In ordinary Avords, they do not appear to have extricated 

 themselves from the true Plover group to the same extent 

 as the aberrant types just enumerated, and, so far as one 

 can as yet form an opinion, they must be looked upon as 

 "true Plovers'' and classified with the true Limicolse 

 (Charadriidse + Scolopacidse). An alternative view is to 

 regard them as standing at some point between the true 

 Limicolse and the Laro-Limicolse (Sheath-bills, Crab-Plovers, 

 Pratincoles, Skuas, Gulls, Terns, &c.), but very much nearer 

 the former than the latter. The Oyster-catchers, indeed, 

 seem to stand in about the same relation to the true Plovers 

 (Charadriidse) as the much-specialised Woodcocks do to 

 such a generalised scolopacine type as the Chatham Island 

 Snipe {cf. 'Ibis,' Oct. 1915, pp. 690-716). 



(2) In the embryo Sheath-bill (Chionarchus) the mor- 

 phology of the lacrymal and frontal region was found to 

 be both interesting and instructive. Unlike what ob- 

 tains in the adult Sheath-bill {cf. 'Ibis,' 1916, p. 144, 

 and text-figure 3), the superior or orbital portion of the 

 lacrymal in the embryo has the form of a thin Ungulate 

 plate of cartilage, which has a free and independent exist- 

 ence laterad of the nasals, and there is not the slightest 

 hint at fusion between the two bones {of. text-figure 7 A). 



In the adult Sheath-bill the identity of the lacrymal of 



