APPENDIX. 



Art. VIII. — A New. Cretaceous Bird allied to Hesperomis / 

 by O. C. Marsh. 



The genus Hesperomis and its near allies have hitherto 

 been found only in a definite horizon, the Pteranodon beds, in 

 the Cretaceous of Kansas, and all now known have been 

 described and figured by the writer.* Recent researches in 

 the Cretaceous of Montana have brought to light another form 

 distinct from Hesperomis, and of smaller size, but evidently 

 belonging to the same general group of gigantic swimming- 

 birds. A. single specimen only has been found, associated with 

 marine fossils of Fox Hills types, and certainly from a much 

 higher horizon than that in which Hesperomis occurs. 



The specimen secured is represented one-half natural size in 

 the figures below, and is a most characteristic part of the 

 skeleton. It is the lower half of the right tibia of a fully 

 adult bird. It shows that the tibia as a whole was very long 

 and slender, with the shaft hollow throughout. In its general 

 features, the specimen resembles most nearly the correspond- 

 ing part in Hesperomis. The general pixyportions of the two 

 are similar. The cavity in the shaft of each is equally exten- 

 sive, and is bounded by smooth, well-defined walls. The 

 ridge for the fibula is equally developed, indicating that this 

 bone was proportionately of the same length in both, and 

 probably of the same form. 



* Odontoraithes, 4to, Washington, 1880. 



Am. Jour. Sci. — Third Series, Vol. XLV, No. 265. — January, 1893 

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