288 University of California Publications in Zoologij I Vol. 13 



c) Summary 



The ostriches, in addition to the characters common to all Ratitae, 

 have the following characters : 



(1) Aftershaft absent, 



(2) Types of barbules similar on all feathers of both nestling 

 and adult. 



(3) Barbules of elongate, ribbon-like form, more or less inter- 

 mediate between an ordinary downy and a pennaeeous type, but dif- 

 ferent from either, with no differentiation of base and pennulum, 

 and no barbicels except rudimentary prongs in body feathers. 



(4) Possibility of their not being derived from flight birds 

 strongl}^ suggested by epiphyology. 



2. Order RHEIFORMES 

 PI. 13, Fig. 1 



Although grouped as a separate order of the Ratitae, equivalent 

 to any of the other three, the rheas are much more closely related 

 to the ostriches than are either to any others of the Ratitae, espe- 

 cially as regards their epiphyology. 



Rheas agree with ostriches, in addition to the common ratite 

 characters, in (1) the large number of primaries (12 to 16 in Rhea), 

 (2) the reduction of the under wing coverts, they being totally 

 absent in Rhea, (3) the absence of aftershafts, and (4) the type of 

 barbules, which, as in ostriches, are intermediate between downy 

 and pennaeeous barbules. The chief differences between the two 

 groups in general epiphyologic characters are: (1) the absence of 

 well-developed rectrices in Rhea, (2) the more obtuse angle made by 

 the attachment of the phalangeal primaries in Rhea; (3) the approach 

 to the carinate type of the relation of the remiges to the arm bones; 

 and (4) the better development of the feathers of the head and neck. 



The details of structure of the feathers, as compared with 

 ostriches on the one hand and carinate birds on the other, are 

 exceedingly interesting. 



a) Rhea americana 



(1) Rem ex 

 Shaft, unlike its condition on some ostrich feathers, finely ridged 

 and grooved on ventral side, with no large conspicuous groove in 

 middle. As a rule, the shaft not as short or heavy relative to feather 

 as in ostriches. 



