186 THE POPULAR SCIENCE MONTHLY. 



position, from the earlier more generalized to the latest comparatively 

 specialized forms, thus affording one of tbe most complete pieces of 

 evidence that are known in favor of a progressive alteration of form, 

 not only of specific, but even of generic importance through advanc- 

 ing ages." The probable home of tbe Camelida? has been revealed in 

 tbe discovery of llama-like creatures, gigantic mammals, in some cases 

 exceeding tbe elephant in size, but with a diversity of characters 

 hitherto unseen either in recent or fossil forms, combining as they did 

 the characters of perissodactyle and proboscidia*n. 



A numberless variety of Carnivora, many of them embracing the 

 most generalized groups, have been brought to light, such as creat- 

 ures between the wolf and the opossum, generalized dogs, and sabre- 

 toothed cats. 



A great many species belonging to the Rodentia, Insectivora, and 

 Chiroptera, have been identified ; still more wonderful is a group of 

 creatures so unlike any beast heretofore known that Prof. Marsh has 

 made a new order to include them under the name of Tillodontia. 

 They combine the characters of several distinct groups, namely, the 

 carnivores, ungulates, and rodents, and some of them in size equal- 

 ing the tapir. Of great interest also is the discovery of fifteen new 

 genera, belonging to low forms of primates. All of these creatures, 

 embracing hundreds of species, are generalized in a high degree. 

 New orders have been erected to embrace some of them. One has 

 only to understand the specialization of modern animals to appreciate 

 tbe generalized character of these early forms. 



Prof. Marsh has shown that all the ungulates in the Eocene and 

 Miocene had upper and lower incisors ; and, again, that all the Eocene 

 and Miocene mammals, including the Carnivora, had two of the wrist- 

 bones, tbe scaphoid and lunar, as distinct bones. 



The class of birds so long represented as a closed type can no 

 longer occupy that isolated position. Tbe proper interpretation of 

 archaeopteryx has, in the discoveries of Marsh, new interest. He has 

 discovered a number of species of birds, for which a new sub-class is 

 made. This sub-class will embrace two sub-orders, one in which the 

 creatures had teeth contained in grooves in the jaws ; the other bad 

 true teeth in the sockets. The first were swimming-birds of gigantic 

 size, with rudimentary wings ; the second embraced small birds, witb 

 powerful wings and bi-concave vertebra?. 



Prof. Cope has also brought to light a remarkable gigantic bird 

 from tbe Eocene of New Mexico ; its size indicates a species with feet 

 twice as large as those of the ostrich. He shows it to be distinct from 

 any of tbe genera of Struthionidce or Dionornithidce. Besides all these 

 wonders, a host of new forms of reptiles and fishes have been discov- 

 ered by these indefatigable explorers huge pterosauria discovered by 

 Marsh with a spread of wing of twenty-four feet ; and of more special 

 interest is the fact that no trace of teeth can be found in the jaws. 



