1951] 
Christiansen — Alaskan Collembola 
129 
side, with four being the most common number. In no case 
were more than four lobes observed on one side. Another 
common variation is the presence of two accessory bosses. 
In other specimens the boss may be very indistinctly 
demarcated. 
The setae of all parts vary considerably, in all ways. The 
antennal olfactory hairs are fairly constant, but the short 
truncate hairs vary from slightly truncate to distinctly 
clavate and from five to eighteen in number. The sensory 
rods of the third antennal segment are always bent, but, as 
shown in the figure, do not always have a marked boot 
shape. The head and body clothing varies considerably, but 
the long ciliate setae are fairly constant, although the degree 
of ciliation and the size vary greatly. 
The mucro also exhibits a good deal of variation, with 
some specimens having the external lamella expanded 
greatly basally, producing the effect of a distinct lamellar 
tooth. The anal horns vary in size, but in all cases observed 
were at least slightly smaller than the ventral edge of the 
third unguis. The horns plus the papillae are usually sub- 
equal to the ventral edge of the claw, but in some specimens 
were as much as one and one-fourth times as long. 
Relationships 
Although, as Stach suggests, the genus Schaefferia is, as 
presently constituted, probably polyphyletic in its make-up, 
the present species appears to be quite closely related to 
the Schaefferia emucronata group (Absolon, 1900). The 
reduced number of eyes, the shape of the P.A.O. and ac- 
cessory boss, the sparsely ciliate setae, the shape and size 
of the unguis, as well as the facies, all suggest a very close 
relationship. While a definite determination of the exact 
relationships among all the members of the S. emucronata 
complex will await a fairly complete collection of the 
Holarctic region, I feel justified in calling the present 
specimens a new species for the following reasons: a) the 
presence of short truncate hairs on the fourth antennal 
segment, not mentioned in any form of S. emucronata or 
S. pouadensis Delamare-Deboutteville, (1945) ; b) the 
much greater development of the furcula; c) different 
