ART. 5. FOSSIL BIRDS FROM ARIZONA WETMORE. 1 3 



the western part of the Mississippi Valley, Central America, and 

 the West Indies, south into South America. It is recorded in small 

 numbers from the Atlantic coast, and is casual in occurrence in 

 British Columbia. The species has not been recorded from Arizona. 



The discovery of Micropalama hesternus is interesting as the stilt 

 sandpiper has stood as the representative of a monotypic genus. 

 The differences between hesteriius and him^ntopus as shown by the 

 head of the humerus are slight but appear constant as a series of five 

 humeri of M. Mmanto'pus at hand seems sufficient to illustrate in- 

 dividual variation in that species. It is possible that M. hesternus 

 may have represented a well-marked western form of M. himantopus. 

 On this supposition the case of the stilt sandpiper would be similar 

 to that of Macrorhamphus griseus^ C atoptrophorus semipalmafus, 

 and Tringa solitaria, shore birds that to-day are represented by 

 eastern and western subspecies. 



The identification of hesternus as a member of the genus Micro- 

 palama led to a review of the humerus in all of our Charadriiformes 

 and brought out an interesting similarity in the form of the 

 humeral head in the turnstones (Arenaria) and the stilt sandpiper 

 a similarity that is astonishing as the two groups are not closely 

 allied (usually they are placed in separate families), and to be 

 explained probably as convergent evolution. So close are the two 

 in form {Arenaria has a longer, heavier humerus) that it was only 

 after considerable study that the following key was worked out to 

 distinguish the two genera. The differences outlined are largely 

 relative, adding to the difficulty in distinguishing the two from 

 disparity in size of the humerus in the two groups. 



a\ Coraco-humeral groove more shallow, less sharply" defined at inner end, 

 inner part of proximal margin straight, with little or no overhang 

 below incisura capitis ; anterior outer margin of fossa subtrochanterica 

 below tuberculum inferior less hooked ; tuberculum inferior relatively 

 less prominent; ridge of tuberculum externum nearly straight with 

 very slight median excavation. 



Arenaria. 



a*. Coraco-humeral groove deeper, more strongly impressed at inner end. 

 anterior (proximal) margin slightly arcuate with distal overhang; 

 angle below tuberculum inferior more hooked ; tuberculum inferior 

 relatively more prominent ; ridge of tuberculum externum excavated in 

 median portion. 



Micropalama. 



Family COLUMBIDAE. 



CHLOROENAS MICULA, new species. 



Characters. — Distal part of tarso-metatarsus similar to that of 

 Chloroenas fasciata (Say), but considerably smaller; external projec- 

 tion (ala interna) on inner trochlea more acute; inner trochlea less 

 deeply grooved on posterior surface ; inner margin with outline show- 

 20183— 25— Proc.N.M.vol.64 5 



