SCIENCE. 



99 



" In June of the following year, the writer again visited 

 the same region, with a larger party, and a stronger es- 

 cort of United States troops, and was rewarded by the 

 discovery of the skeleton which forms the type of Hes- 

 perornis regalis, Marsh. Various other remains of 

 Odontornithes were secured, and have since been de- 

 scribed by the writer. Although the fossils obtained 

 during two months of explorations were important, the 

 results of this trip did not equal our expectations, owing 

 in part to the extreme heat (i io° to 120 Fahrenheit, in 

 the shade) which, causing sun stroke and fever, weak- 

 ened and discouraged guides and explorers alike. 



" A considerable part of these Cretaceous deposits still 

 remain unexplored, and in the Autumn of 1872, a third 

 expedition through this territory was undertaken by the 

 writer with a small party. Additional specimens of 

 much interest were secured, including the type of the 

 genus Apatornis, and one nearly complete skeleton of 

 Hesperornis — an ample reward for the hardship and dan- 

 ger we incurred. 



" The specimens thus secured by these various expe- 

 ditions have since been supplemented by important ad- 

 ditions, collected in the same general region by different 

 parties equipped and sent out by the writer, who no lon- 

 ger could give his personal supervision to work in that 

 fiield. The fossil birds procured in this region, since 

 1870, by these different expeditions, include remains 

 of more than one hundred different individuals of the 

 Odontornithes. These are all in the Museum of Yale 

 College, and form the material on which the present vol- 

 ume is based. 



" A study of this extensive series of bird remains 

 brings to light the existence, in this class, of two widely- 

 separated types, which lived together during the Cre- 

 taceous period, in the same region, and yet differed more 

 from each other than do any two recent birds. Both of 

 these types possessed teeth, a character hitherto unknown 

 in the class of. birds, and hence they have been placed by 

 the writer in a separate sub-class, the Odontornithes. 

 One of these groups includes very large swimming birds, 

 without wings and with the teeth in grooves (Odontolcce), 

 and is represented by the genus Hesperornis. The other 

 contains small birds, endowed with great powers of 

 flight, and having teeth in sockets (Odontotomies), and 

 biconcave vertebrae ; a type best illustrated by the genus 

 Ichthyornis. Other characters, scarcely less important, 

 appear in each group, and we have thus a vivid picture 

 of two primitive forms of bird structure, as unexpected 

 as they are suggestive. A comparison of these two 

 forms with each other, and with some recent birds, 

 promises to clear away many difficulties in the genealogy 

 of this class, now a closed type ; and hence they are wed 

 worthy of the detailed description and full illustration 

 here devoted to them. 



" The fossil birds now known from the Cretaceous de- 

 posits of this country are included in nine genera- and 

 twenty species. These have all been described by the 

 writer, and are represented, at present, by the remains 

 of about one hundred and fifty different individuals. This 

 is evidence of a rich and varied avian fauna in America 

 during Mesozoic time, and likewise indicates what we 

 may expect from future discoveries. 



" The present volume is the first of a series of Mono- 

 graphs designed to make known to science the extinct 

 vertebrate life of North America. In the investigation of 

 this subject, the writer 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 work- 

 ing 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 unfolded, that a plan of gradual publica- 

 tion became a necessity. The more important discover- 

 ies were briefly announced soon after they were made, but 



only where the specimens on which they were based ad- 

 I mitted of accurate determination. The principal charac- 

 ters of the new groups were next worked put systematic- 

 ally, and published with figures of the more important 

 parts. When the investigation of a group is completed, 

 the results, with lull descriptions and illustrations, 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 result 

 will soon be ready for publication. 



" The material is abundant for a series of monographs 

 on the marvelous 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 described by other authors, 

 but at least one-half remain to be investigated. 



" Among the new groups brought to light by these re- 

 searches, 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 Pterano- 

 don. Of this group, remains of more than six hundred 

 individuals are now in the Yale College Museum — ample 

 material to illustrate every important point in their os- 

 teology. 



" With these fossils were found also great numbers of 

 Mosasauroid reptiles, a group which, although rare in 

 Europe, attained an enormous development in this 

 country, both in numbers and variety of forms. Remains 

 of more than fourteen hundred individuals belonging to 

 this order were secured during the explorations of the 

 last ten years, and are now in the Museum of Yale Col- 



le e e - 



"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 ani- 

 mals yet discovered. Another remarkable group of large 

 reptiles found in the same formation were the Stego- 

 saitria. Other Dinosaurs from the same horizon, the 

 ' Atlantosaurus beds,' show that this was the dominant 

 form of vertebrate life in that age, and many hundred 

 specimens of these reptiles are now in the Yale Museum. 

 In a lower horizon of the same formation, the ' Saurano- 

 don beds,' were found the remains of a peculiar new 

 group of reptiles, the Sauranodontia, allied to Ichthyo- 

 saurus, but without teeth. 



" In the Eocene deposits of the Rocky Mountains, the 

 writer discovered a new order of huge mammals, the 

 Dinocerata. Remains of several hundred individuals 

 were secured, and a monograph on the group will follow 

 the present memoir. In the same formation were found 

 the remains of another new order of mammals, the Tillo- 

 dontia, in many respects the most remarkable of any yet 

 discovered. In the same Eocene deposits were secured 

 the first remains of the fossil Primates known from North 

 America as well as the first Cheiroptera and Marsu- 

 pialia. Abundant material also was found in the same 

 region to illustrate the genealogy of the Horse, and a 

 memoir on this subject is in course of preparation. 



Cholesten. — This compound. C 2 6H 45 , is a white amor- 

 phous powder, almost insoluble ir. alcohol, but soluble in 

 ether. It resembles c. cholesterin in its physical and chem- 

 ical properties. — W. E. Walitzky. 



