Extinct Toothed Birds of North America. 523 
has spent the past ten years, much of it in the field, collecting, with 
no little hardship and danger, the material for study, and the rest in 
working out the characters and affinities of the ancient forms of 
life thus discovered. 
During this decade, the field work, extending from the Missouri 
River to the Pacific Coast, has so predominated, as the subject un- 
folded, that a plan of gradual publication became a necessity. The 
more important discoveries were briefly announced soon after they 
were made, but only where specimens on which they were based 
admitted of accurate determination. The principal characters of the 
new groups were next worked out systematically and published, 
with figures of the more important parts. When the investigation 
of a group is completed, the results, with full descriptions and illus- 
trations, will be brought together in a monograph. This system has 
been carried out with the Odontornithes, and will be continued with 
the other groups. The investigation of several of these is now nearly 
completed, and the results will soon be ready for publication. 
The material is abundant for a series of monographs on the mar- 
vellous extinct vertebrates of this country, and the results already 
attained are full of promise for the future. A somewhat careful 
estimate makes the number of new species of extinct vertebrates 
collected since 1868, and now in the Yale College Museum, about 
1000. Nearly 300 of these have already been described by the 
writer, and some have been noticed or deseribed by other authors, 
but at least one-half remain to be investigated. 
Among the new groups brought to light by these researches, and 
already made known by descriptions of their principal characters, 
are the following, which will be fully described in subsequent 
volumes of the present series. 
The first Pterodactyles, or flying reptiles, discovered in this 
country, were found by the writer in the same geological horizon 
with the Odontornithes, described in the present memoir. These 
were of enormous size, some having a spread of wings of nearly 
twenty-five feet ; but they were especially remarkable on account 
of having no teeth, and hence resembling recent birds. They form 
a new order, Pteranodontia, from the type genus Pteranodon. Of 
this group, remains of more than six hundred individuals are now in 
the Yale College Museum—ample material to illustrate every im- 
portant point in their osteology. 
With these fossils, were found also great numbers of Mosasauroid 
reptiles, a group which, although rare in Europe, attained an 
enormous development in North America, both in numbers and 
variety of forms. Remains of more than fourteen hundred indi- 
viduals, belonging to this order, were secured during the explora- 
tions of the last ten years, and are now in the Museum of Yale 
College. 
The most interesting discoveries made in the Jurassic formation 
were the gigantic reptiles belonging to the new sub-order Sauropoda, 
including by far the largest land animals yet discovered. Another 
remarkable group of large reptiles found in the same formation were 
