ACARINA FROM THE JUAN FERNANDEZ ISLANDS 563 



the genus (fig. 12) and resemble especially ihos,e o^ Neoliodes vermiailatus ]\CO'Y 

 {1924, fig. 2) although the relative size of the shields is quite different. Thus 

 the relative length of the 4 shields is expressed by i; 1.34; 1.65; 1.95 in N. Back- 

 stromi, while in N. venniadatus JaCOT it is expressed by i; 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 

 (1. 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 N. Bdckstrdnii 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 striae 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 striae and anteriorly a median portion where the 

 striae are missing, and the texture is almost smooth with some punctures. The 

 3rd nymphal girdle has anteriorly a broad portion, about 2V2 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. 



