INTRODUCTION 8&7 
from among the earth’s inhabitants, has thrown a comparatively broad 
beam of light through the darkness that, broken only by the solitary spark 
emitted on the recognition of Archzxopteryx, had hitherto brooded over our 
knowledge of the genealogy of Birds, and is even now for the most part 
palpable. Subsequent visits to the same part of North America, often 
performed in circumstances of discomfort and occasionally of danger, 
brought to this intrepid and energetic explorer the reward he had so 
fully earned. Brief notices of his spoils appeared from time to time in 
various volumes of the American Journal of Science and Arts (Silliman’s), 
but it is unnecessary here to refer to more than a few of them. In that 
Journal for May 1872 (ser. 3, ill. p. 360) the remains of a large swimming 
Bird (nearly 6 feet in length, as afterwards appeared) having some affinity, 
it was thought, to the Colymbidx were described under the name of Hesper- 
ornis regalis, and a few months later (iv. p. 344) a second fossil Bird from 
the same locality was indicated as Ichthyornis dispar—trom the Fish-like, 
biconcave form of its vertebre. Further examination of the enormous 
collections gathered by the author, and preserved in the Museum of Yale 
College at New Haven in Connecticut, shewed him that this last Bird, 
and another to which he gave the name of Aputornis, had possessed 
well-developed teeth implanted in sockets in both jaws, and induced 
him to establish for their reception a “Subclass” ODoNTORNITHES (page 
649) and an Order Ichthyornithes. Two years more and the origin- 
ally found Hesperornis was discovered also to have teeth, but these were 
inserted in a groove. It was accordingly regarded as the type of a distinct 
Order OpontoLc# (loc. cit.), to which were assigned as other characters 
vertebre of a saddle-shape and not biconcave, a keelless sternum and 
wings consisting only of the humerus. In 1880 Prof. Marsh brought ont 
a grand volume, Odontornithes, being a monograph of the extinct toothed 
Birds of North America. Herein remains, attributed to no fewer than a 
score of species, which were referred to eight different genera, are fully 
described and sufficiently illustrated, and, instead of the ordinal name 
Ichthyornithes previously used, that of ODONTOTORM4 (loc. cit.) was proposed. 
In the author’s concluding summary he remarks on the fact that, while the 
Odontolcx, as exhibited in Hesperornis, had teeth inserted in a continuous 
groove—a low and generalized character as shewn by Reptiles, they 
had, however, the strongly differentiated saddle-shaped vertebra such 
as all modern Birds possess. On the other hand the Odontotorme, 
as exemplified in Ichthyornis, having the primitive biconcave vertebre, 
yet possessed the highly specialized feature of teeth in distinct sockets. 
Hesperornis too, with its keelless sternum, had aborted wings but strong 
legs and feet adapted for swimming, while Jchthyornis had a keeled 
sternum and powerful wings, but diminutive legs and feet. These and 
other characters separate the two forms so widely as quite to justify 
their assignment to distinct Orders, and the opposite nature of the 
evidence they afford illustrates one fundamental principle of Evolution, 
namely, that an animal may attain to great development of one set of 
characters and at the same time retain other features of a low ancestral 
type. Prof. Marsh states that he had fully satisfied himself that Arche- 
opteryx belonged to the Odontornithes, which he thought it advisable for 
