1877.] MR. A. H. G.iRROD ON THINOCORUS AND ATTAGIS. 



417 



therefore considered certain, notwithstanding the partial resemblance 

 of their vomers. 



Next with reference to Chionis. By De Blainville this genus has 

 been located close to HtBmatopus^ ; and his view has been accepted, 

 to a greater or less extent, by many. Nevertheless, although these 

 birds are both strictly schizorhinal, their skulls give indications of a 

 very different affinity. Hcematopus possesses supraoccipital foramina, 

 as well as pterygoid articulations with the basispbenoid, together with 

 a bifid vomer, as represented in fig. 2. The similarly formed vomer is 

 extraordinarily broad in Recurvirostra avocetta, which is shown ia 



W / 

 Anterior extremity of vomer in : — 1. Sterna hirundo ; 2. HcBmatopus ostralegns; 

 3. Numenius arquatiis ; 4. Recurvirostra avocetta ; 5. Chionis alha. 



fig. 4, agreeing with the restricted Limicolae ; whilst in Chionis the 

 vomer is blunt (fig. 5), and the basispbenoid rostrum, as well as the 

 pterygoids, are entirely free as far as articulating facets are con- 

 cerned. In the Bulletin of the United States National Museum^ Dr. 

 E. Coues and Mr. Kidder, after a most careful study of the whole 

 anatomy of the genus, Chionis minor especially, remark, "We find 

 in Chionis a connecting link, closing the narrow gap between the 

 plovers and gulls of the present day. In our opinion this group 

 represents the survivors of an ancestral type from which both gulls 

 and plovers have descended"'. A separate division,- termed Chio- 

 nomorphee, is established for them, comparable with the Gerano- 

 morphse and the Cecomorphse of Prof. Huxley*. My dissections of 

 both C. alba and G. minor are quite in favour of this Larine affinity. 

 That the genus deserves to be located in a separate division, however, 

 as Dr. Coues suggests, I cannot agree. The Cecomorphse of 

 Prof. Huxley include the Laridse, Procellariidae, Colymbidse, and 

 Alcidse ; and it is now known that neither the Procellariidae nor Co- 

 lymbidse come near the Laridse and Alcidae, which two last-named 

 families are related one to the other most intimately, and differ from 

 one another to almost exactly the same amount as the Chionididse do 

 from either. I should place the Chionididse, the Laridse, and Alcidss 



' Anuales des Sciences Naturelles, yi. 1836, p. 97. 



' No. 3, p. 85, Washington, 1870. » L. c. p. 114. 



♦ P. Z. S. 18G7, p. 4.57. 



Proc. Zool. Soc— 1877, No. XXVII. 27 



