ACARINA FROM THE JUAN FERNANDEZ ISLANDS 563 
the genus (fig. 12) and resemble especially those of Neolzodes vermiculatus JACOT 
(1924, fig. 2) although the relative size of the shields is quite different. Thus 
the relative length of the 4 shields is expressed by 1; 1.343 1.65; I.95 in VV. Back- 
stromz, while in WV. vermiculatus JACOT it is expressed by 13 1.57; 1.75; 2.62. 
These shields are the dorsal plates of the 4 developmental stages of the 
species, which during the ecdyses obviously split along the band of thin, trans- 
versally striated cuticle which separates them from the ventral plate. When the 
animal is fullgrown rests of this band still remain attached to the last nymphal 
shield at least along the sides (comp. fig. 12). 
From the way this shield is formed it is evident that the whole dorsal 
side remains, although only a peripheral girdle is more strongly chitinized and 
corrugated. As a matter of fact it is easy by treating the shields with boiling 
lactic acid to separate them from one another. We notice then an exceed- 
ingly thin and almost hyalin central part on each shield. In some species a 
projection of the 3rd nymphal skin penetrates through an oval opening in the 
2nd skin but the 2nd and Ist nymphal skins are whole. 
It is, therefore, difficult to understand what JACOT means, when he says 
(l. c. p. 79): »These girdles are not the peripheral girdle of a complete skin 
but are, in themselves the complete new skin, thus each skin (after the first) 
consists, not of a disc or saucer or cap-like covering, but of a girdle beginning 
where the previous one terminated. The removal of any of the skins leaves 
a clear, smooth area.» 
As a matter of fact the opposite is true, because the girdles are only the 
thickened marginal portions of the dorsal skin, which remains, a fact which 
one would be able to infer a priori, since it seems impossible to conceive who 
the central portion could disappear, when it is covered by the shield of the 
earlier stage. In NV. Backstrom the inner part of the last girdle (3rd nymphal) 
is covered by that of the penultimate girdle. 
The larval skin has in the posterior half an elongated oval area, which is 
the top of the entire shield. This area has 2—4 faint longitudinal ridges; 
further forwards are 6 A-shaped ridges, the lateral ends of the two anterior 
ones being coalesced. The Ist nymphal girdle has a number of about 40 radiat- 
ing strie and has anteriorly a median portion about twice as broad as the 
diameter of the girdle, where the striae are missing and there is a transverse 
‘loop, paralell to the foremost ridge of the larval shield. The 2nd nymphal 
girdle has similar radiating striz and anteriorly a median portion where the 
strie are missing, and the texture is almost smooth with some punctures. The 
3rd nymphal girdle has anteriorly a broad portion, about 2'/2 times as long 
as the diameter of the girdle, where the texture is reticulated owing to num- 
erous round depressions in the cuticle. 
Mouthparts (Fig. 14). The hypostome is large, about 50 % broader 
than it is long, pentangular, with converging sides, obtusely angular posterior 
edge and slightly concave anterior edge. The surface is sculptured by very 
irregular ridges running in all directions, but a rim along the margin is smooth 
without any sculpture. The two hypostomal hairs are short, pointed and in- 
serted near the median line far forwards, a little nearer to the anterior margin 
than their own length and slightly further apart. 
