NO. II CLASSIFICATION, BIRDS OF THE WORLD — WLTMORE 5 



classification, though it has been my belief from the beginning that it 

 was reptilian. It is known from a lower jaw, beautifully preserved, 

 without appreciable deformation and practically complete except for 

 part of the lower section of one ramus. The resemblance to birds is 

 found in the lack of teeth, fused symphysis, and the considerable size 

 of the mandibular foramen. While these are characters found in 

 birds, there is nothing peculiar included since all are duplicated in some 

 of the groups of the Reptilia. The fossil resembles Reptilia in the 

 form of the articular surface, the forward position of the coronoid 

 area, the conformation at the symphysis, especially on the upper 

 surface, the upward curvature in that area, and in the general texture 

 of the bone. In none of these is there exact duplication in Aves, 

 except partially in the form of the symphyseal region. The whole 

 appearance of the bone strongly suggests a species related to the 

 Ornithomimidae among the therapod dinosaurs. In view of this the 

 "Order Caenagnathi formes" is now omitted from the avian classifica- 

 tion, since it is felt that its continued tentative inclusion may promote 

 misunderstanding as to its status. 



The family Eleutherornithidae is introduced for the fossil Eleu- 

 therornis helveticus Schaub, from the Eocene of Switzerland, de- 

 scribed from a fairly well preserved pelvis. Apparently this is repre- 

 sentative of an ancestral group from which the living ostriches may 

 have come. Its greatest importance is found in its indication of re- 

 lationship with carinate groups though of unquestioned ratite stock. It 

 is thus important as definite indication that the struthious birds are 

 descended from flying ancestors, not from some distinct cursorial line 

 that always has been flightless, as some have contended. 



The genus Podiceps. — The differences of opinion that prevailed for 

 years as to the application of the generic name Colymbus have been 

 adjusted currently by an arrangement under which Gavia has been 

 accepted for the loons and Podiceps for the grebes. There is, how- 

 ever, discussion still as to the proper spelling of the ordinal and 

 familial names for which Podiceps is the base. The uncertainty arises 

 from misunderstanding of the derivation of this generic term. The 

 colloquial name applied to these diving birds in the English of the 

 16th to the 18th centuries (and later) was "arse foot," or "arsfoot," 

 from the posterior position of the leg. The term is found in the early 

 dictionaries of Johnson, was carried in the later editions of Todd and 

 Walker, and is still found in a footnote in Webster's 1953 volume, 

 with indication there that the word now is obsolete. Some early 

 authors who wrote in Latin rendered this term appropriately as 

 "Podicipes," as for example Willughby (1676, p. 258), and Ray (171 3, 



