86 
Lucas on the Os Prominens. 
olive-green on the upper parts, they fully equal any of the California fe- 
males. The supposed difference in the tail markings of these races does 
not hold in the series before me, for a male from Nicasio has the edging 
on the inner webs of the rectpces quite as broad and pure as that of any of 
the Florida ones. The loss of this character, however, would be of little 
consequence, as the two forms could be readily separated by the wide dif- 
ference in their general coloring. Mr. Henshaw considers his Arizona 
specimens true celata , and lutescens is now for the first time announced 
from that Territory. 
290, $ ad., Tucson, April 26. Length, 5; extent, 7.30; wing, 2.45; 
tail, 2.10. “ Iris dark brown ; bill black, lighter at base below; legs dark 
brown. Not common.” 
291, $ ad., same locality and date. Length, 4.70; extent, 7.10; wing, 
2.37 ; tail, 2.09. Same remarks. 
( To be continued *) 
NOTES ON THE OS PROMINENS.* 
BY FREDERIC A. LUCAS. 
My attention was first directed to this bone by Dr. Shufeldt’s 
article in this Bulletin for October, 1S81 , and subsequently by Mr. 
Jeffries’ paper in the number for January, 1882. With the view 
of ascertaining in what birds the os prominens is present, and 
what is its use, I have since examined quite an extensive series 
of birds. Lack of time has prevented as extended an examina- 
tion as could be wished for ; and as regards discovering any spec- 
ial use for this sesamoid, it must be confessed that the results of 
the investigation are not wholly satisfactory, being rather negative 
than positive in their character. But such as they are, they are 
submitted, in the hope that they may prove of service to some 
better skilled physiologist. 
Through a lack of good material Dr. Shufeldt failed to dis- 
cover the existence of the os prominens in any of the Owls, but 
it would seem to be specially characteristic of the Bubonidce , 
since it is present in one particular shape, and with a constant 
mode of articulation, in the following species of that family: 
Ketufia ceylonensis , K. javanensis , Bubo ignavus , B. bengal- 
* The name “os prominens,” proposed by Dr. Shufeldt, has been adopted by me 
because it seems eminently proper that so large a sesamoid, frequently equalling the 
patella in size, should receive a distinctive appellation. 
