64 The American Geologist. Jan. isol 
mark that remains is the presence of feathers "which -av^ totally un- 
known among reptiles. " Even this test however would fail if some oi 
the earlier feathered forms were ranked (as they well might be, this- 
single character apart) with reptiles. One of the most remarkable' 
chapters in palaeontology and in the evolution of animal life is that in 
which is traced the discovery of the forms intermediate between these 
two groups. Scarcely a link is missing. ArchOBOpteryx, the reptile 
bird of Solenhofen. led the way, if we omit some possibly avian foot- 
prints in the Connecticut valley, and was. after a long interval, followed 
by the toothed Hesperornis of North America, the toothless Aepyornis 
of Madagascar, and the Apteryx of New Zealand. 
Among the carinate birds to which most of the existing species belong 
we have also a toothed and a toothless series, the former extinct and 
consisting only of the genus Ickthyomis which the author places here, 
rejecting the order of Odontorniihes proposed by Marsh to include this 
and Hesperornis. 
The toothless division of th<' car mates includes a number of forms- 
many of which are almost recent, some having been exterminated by 
the agency of man. None are older than the Cretaceous and by far the 
greater number are only of Tertiary age. They include among others 
a penguin, the great auk. woodcocks and plovers, bustards, cranes and 
rails, turkeys, pheasants, and grouse, quails and pigeons, the Dodo of 
Mauritius, geese and ducks, albatrosses and frigate-birds, vultures, fal- 
cons, and buzzards, owls, parrots and cockatoos, kingfishers, woodpeck- 
ers, swallows, sparrows, crows, etc. 
On the whole the story of the evolution of the bird is the most won- 
derful that has been read to us by the paleontologist and it has been 
well brought up to date by the author. The type specimens are scat- 
tered in the various museums over so large an area, and the literature 
of the subject is dispersed in the journals and proceedings of so many 
scientific societies, that it has been no light task to collect it as he has 
here done. 
Of the characters of the Mammalia a few only can be employed in 
pakeontology — those for the most part belonging to the hard parts of 
the body. The double articulation of the cranium with the atlas, the 
firm union of the rami of the lower jaw, the absence of a quadrate bone 
and of a moveable joint between the proximal and distal tarsal bones 
are the most important and useful. The structure of the teeth is of the 
first value, both for the identification of fossil forms, and for the tracing 
of ancestral lines. As might be expected from the author's long experi- 
ence, and great familiarity with his subject, the work is well down to 
date in these respects. All the latest researches on the evolution of the. 
multitubercular mammalian tooth from that simpler conical and uni- 
tubercular tooth that characterized the reptilian predecessors and an- 
cestors of the Mammalia are brought into service, and it is easy to per- 
ceive that though many gaps still remain, yet the line of the develop- 
ment of these organs is rapidly being traced and Idled. These results- 
