or Toothed Birds of North America. 275 
perfect circulation. A true bird would doubtless require 
arm blood, but would not necessarily be hot-blooded, like 
the birds now living. 
shoot. It is probable that Hesperornis came off from the main 
Struthious stem, and has left no descendants. 
“These three ancient birds, so widely different from each 
other, and from all modern birds, prove beyond question the 
marvelous diversity of the avian type in Mesozoic time; an 
also give promise of a rich reward to the explorer who success- 
fully works out the life-history of allied forms, recorded in 
ages more remote.” 
tigations upon this and kindred points, we may fairly hope 
that future discoveries will add much to our knowledge of this 
Professor Geikie’s remark in regard to them. He says:— 
They are strictly and rigidly scientific diagrams, wherein 
®very bone and part of a bone is made to stand out so clearly 
that it would not be difficult to mold a good model of the skel- 
