400 ■ ME. W. p. PTCRAPT ON THE 



most nearly resembles JSizmra in this matter. It is a curious 

 fact, that in tlie Mergansers, where one would expect to find 

 these processes extremely well-developed, they are, on the con- 

 trary, smaller and fewer than in any other diving ducks — 

 numbering but 5, and having very small X-shaped processes. 

 Taken in conjunction with the fact that these birds differ also 

 fi'om the sea-ducks in the absence of supra-orbital depressions 

 for the supra-orbital gland, it would almost seem as though their 

 partially marine habitat had been adopted quite recently. 



Outside the Anseres, hypapophyses occur in the Penguins, 

 Grebes^ » Divers, Cormorants, and Alcidse, all types which dive 

 for their food. 



In the Penguins the hypapophyses 1-3 have their free ends 

 expanded to form the horizontal plates described in Biziura ; 

 behind these follow 4 simple processes. In the Divers these 

 expanded free ends occur on 1-2 — where they are very large — 

 and 3, where they are small ; beliind these follow 4 simple 

 spines. In the Grrebes — freshwater divers — spines 1-3 have 

 feeble lateral plates and the rest simi^le. The Alcidse (Guille- 

 mots, Auks, &c.) have extremely well-developed hypapophyses. 

 Here 1-4 have very large lateral plates, 5-8 are simple. In the 

 Cormorants ifc is somewhat surprising to find all the hypapophyses 

 1-7 of the simple type — there are no lateral plates. In the 

 Gannet, Pelican, Prigate-birds, &c. these spines are altogether 

 wanting, and this because though they swim much, yet they 

 do not dive. Thus we have a parallel to the case of the Geese 

 and Swans among the Anseres. 



The vertebral centra in these diving birds are much com- 

 pressed laterally. 



The Shouldek-Giedle aistd Sternum. 

 There are no points calling for special comment in the 

 shoulder-girdle of Biziiira. The sternum does not exactly 

 agree with that of any other duck with which I have compared 

 it. The spina externa and interna are wanting. The posterior 

 lateral processes are free, short, and curved, and project beyond 

 the level of the metasternal border. In that these processes are 

 free they resemble those of Erismatura, Somateria^ and O^demia, 

 Dendrocygna, and the Geese and Swans. That is to say, in this 

 character these birds represent a less specialized condition 

 than that which obtains in the Ducks generally, where the free 



