288 University of California Publications in Zoology  \Vor. 18 
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 pennaceous 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 
strongly suggested by epiphyology. 
2. Order RHEIFORMES 
Pl. 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 pennaceous barbules. The chief differences between the two 
groups in general epiphyologie 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 earinate birds on the other, are 
exceedingly interesting. 
a) Rhea americana 
(1) Remer 
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. 
