434 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 18 



is to be associated with the unit cell. The arrangement is thus a 

 body-centered one (unless a complicated structure having at least 

 eight chemical molecules in the unit cube is to be assumed). ^V 



Calculated density = 4.54. 

 Spacing: <iioo = 4.55±0.015 A. U. 

 Structure: Body-centered grouping (Fig. 2). 



Results of the determinations of the crystal structures of other 



alkali halides will be given in a subsequent number of this JournaIv. 



ORNITHOLOGY. — Three new birds of the family Tinamidae from 



South America.^ Alexander Wetmore, Biological Sun'-ey. 



Study of tinamous in the United States National Museum of the 

 genera Rhynchoins, Nothura, and Calopezus, has led to the identifi- 

 cation of three forms that have been unrecognized hitherto. They 

 may be known from the following detailed descriptions. 



Rhynchotus arcanus, sp. no v. 



Characters. — Similar to Rhynchotus rufescens (Temminck) ; outer webs of 

 three outermost primaries, alula, and both webs of greater wing-coverts 

 barred narrowly with blackish; more heavily barred with black above; 

 bill slightly more slender at base. 



Description. — Type, Cat. No. 21061, U. S. Nat. Mus., adult, sex not known, 

 collected at Parana, Entre Rios, Argentina, March, 1860, by Capt. T. J. 

 Page. Crown black, lateral feathers and those on fore part of crown margined 

 narrowly with chamois, forming an indistinct median stripe on anterior third 

 of crown, median feathers of hinder portion of crown margined with cinnamon; 

 sides of head dull cream-buff, lighter on lores and below eyes, changing to 

 chamois behind eyes ; streak from eye through ear, ear coverts, and a narrow 



" Ralph W. G. Wyckoff and Eugen Posnjak, op. cit. 



' Received October 3, 1921. 



