148 



KECOKDS OF THE AUSTRALIAN MUSEUM. 



thorax has effaced the true outlines of these portions." The 

 embryonic forms of Gamasus, Lati'., and Ixodes, Latr., have foui- 

 pairs of legs before birth, but one pair is aborted to be again 

 developed at the nymphal stage. This Banks regards as an indi- 

 cation that the six-legged larva is a secondary development, and 

 lessens the apparent difference between Acarina and other 

 Arachnids. In Uropoda, Latr., the anterior legs are inserted in 

 the canierostome — the opening of the body into which the mouth 

 parts are inserted. 



Abdomen. — Usually large and devoid of segmentation ; in some, 

 however, segmentation is distinct. The corpus tndva ov ejngynum 

 is of various shapes and sometimes closed by flaps ; male aperture 

 (epiandrum) usually smaller than that of the female. The 

 reproductive system is often highly developed, and frequently 

 occupies a considerable part of the body. 



Respiratory Organs. — For the purpose of i^espiration many 

 species are endowed with an elaborate tracheal system, but there 

 are a large number of forms not provided with such. Amongst 

 those species in which a tracheal system obtains, great vari- 

 ations are displayed. Commonly the tracheae open near the 

 mandibles, but with the Ixodida? and Gamasidae the apertures 

 are near the hind legs. In some species the tracheal openings 

 occur in the coxal cavities (acetahtda). Of those — and the 

 species are many — which have no tracheal system, it has been 

 observed that the skin is soft, and that oxygen is al)Sorbed 

 by osmosis through the general surface of the body. 



The object of the present paper is primarily to draw the 

 attention of Australian students to our rich and extensive Acarid 

 fauna. To this end a list of the known species — endemic and 

 introduced — together with those families which may reasonably 

 be expected to occur, is given below. Species apparently new 

 are described. 



Banks divided the larger groups of the order into eight super- 

 families," which he defined as follows : — 



1. Abdomen annulate, prolonged behind ; veiy minute 



forms ; often with but four legs. . Demodicoidea. 



Abdomen not annulate nor prolonged behind ; always 

 with eight legs 2. 



2. With a distinct spiracle upon a stigmal plate on each 



side of body (usually below) above the third or 



" Banks -Prof. U. States Nat. Mus., xxviii., 1904, p. 10. 



