Fossil Birds in the Marsh Collection of Yale University 11 



the tarso-metalarsus, a compression into which the proximal end or 

 head of the bone does not enter. In fact, the entire tarsus and foot 

 in Hfe presents this lateral compression in such a form as Gavia immer, 

 and, in swimming, it permits a rapid, unimpeded stroke of this part of 

 the pelvic limb through the water, both forwards and backwards. 

 This means increased speed in swimming and diving on the part of 

 these modern pygopodines, a power which I believe they possess 

 quite in excess of either Hesperornis or Baptornis, though in the last 

 two genera the latter exhibits the character better than does the 

 representative of the toothed birds. ^4^ a character, it has become 

 emphasized during the evolvement of the tribe, and a comparative 

 study of the skeleton of the foot in these several birds will convince 

 one of the truth of this. 

 The name Baptornis advenus of Marsh should stand. 



Genus Cimolopteryx Marsh. 

 {Plate VI, Figs. 38, 39.) 



Marsh, Amer. Journ. Sci., ser. 3, XXXVIII, 1889, 83, footnote. Type, by 

 subsequent designation, Cimolopteryx rara Marsh (Hay, 1902). 



Cimolopteryx rara Marsh. 

 (Plate VI, Fig. 38.) 



Marsh, Amer. Journ. Sci., ser. 3, XXXVIII, 1889, 83, footnote; Ibid, XLIV, 

 1892, 175, Plate III, Fig. 2. 



Holotype. Cat. No. 1805, Peabody Museum, Yale University. Converse Co., 

 Wyoming. Cretaceous (Lance). J. B. Hatcher, collector. 



Also: Cat. No. 868, Peabody Museum, Yale University. Converse Co., Wyom- 

 ing. [Cretaceous (Lance). Lull.) 



In his article cited above (Art. XI. "Discovery of Cretaceous 

 Mammalia," p. 81), Professor Marsh briefly describes this material in 

 a footnote, thus "Remains of a single bird were found at one locality 

 in association with the mammals. It was about as large as a pigeon, 

 and had strong powers of flight. ' It appears to be related to Apaiornis, 

 one of the toothed birds described by the writer. It may be called 

 Cimolopteryx rams." 



In the places cited. Marsh gives figures and descriptions which 

 quite fully describes the coracoids of these birds; but in the present 

 species, so far as I have discovered, he did not mention that the proc- 

 ess at the outer sternal angle had been broken off, — ^a process which 

 is present in the coracoids of both Ichlhyornis and Apatornis. The 

 lower margin of the bone is Hkewise chipped. 



