1804. PROCEEDINGS OF THE NATIONAL MUSEUM. 587 



Also the second and third phalanges of the third digit unite. Hence 

 in the Cypselus, notwithstanding that in the early stages of growth the 

 normal number of phalanges for birds, 2-3-4-5, is developed, in this 

 genus the number of phalanges in adults is 2-3-3-3. 



Ptitzner, 1890, discusses the reduction of the number of phalanges 

 in the little toe of man. In embryos and young children he found the 

 normal number of phalanges 3, but in the case of older children the 

 middle and the end phalanges usually unite, though in some instances 

 the middle phalange disappeared. 



In Terrapene I have not been able to determine the method of the 

 reduction in the number of phalanges since embryological material of 

 T. ornata has not been obtained. I hope to be able to investigate this 

 question further at a later date. But, in the examination of younger 

 specimens, I find no evidences of coossification such as would probably 

 be indicated by the disproportionate length of a phalange formed by 

 the union of two phalanges. 



The distribution of the species of Terrapenc presents several interest- 

 ing i>roblems. It seems probable that all of our species are derived from 

 one form. The closeness of the relations of the species would seem to 

 indicate that our forms are varieties rather than species. However, at 

 least two ditficulties are in the way of this conclusion. First, there can 

 be no question but that if we take two extremes of development of the 

 species of the genus, for instance, T. major and T. ornataor T. Carolina 

 and T. ornata., we must recognize them as separate species. But since 

 other intermediate forms seemingly connect these si)ecies, if the close- 

 ness of relations be considered as indicating varietal characteristics 

 only, we are forced to consider all species as varieties, a conclusion that 

 would seem to be erroneous. Second, while the relations indicated 

 by a study of the different species seems close, yet the distinctions 

 seem definite and fixed, even where the ranges of the species overlap. 

 The study of a number of specimens seems to indicate that the different 

 si»ecies are derived from one form, and that afterwards, by isolation, 

 caused possibly by geological and climatic agencies, they became dis- 

 tinct. When we remember the comparatively fixed abode of these 

 animals it seems reasonable to suppose that these changes might have 

 been brought about by relatively simple agencies which need not neces- 

 sarily have acted simultaneously. Hence, it would seem proper to 

 classify each form as a distinct species, each possessing certain fixed 

 osteological characters. If these conclusions be true then it wouhl 

 seem most reasonable to suppose that T. ornata has become more dis- 

 tinct from the other species by its comparatively longer isolation, aided 

 by the generally arid climate of its habitat. 



It Avill at once be noticed that of the species found within the United 

 States each occurs in a district which, in ci'rtain geographical features, 

 is peculiar to itself. T. ornata occupies a district peculiar in its arid 

 climate and, for the most part, sandy soil. T. triunguis is fouad in the 



