228 Transactions of the Society. 



the edge of each of the stigmata always proceeds a hair, the shape 

 of which varies with the species ; it is known as the protecting hair, 

 and I have a few words to say about it hereafter, 



3. The legs have invariably five joints, and are terminated by 

 either one or three claws, without sucker or caroncle. 



4. The palpi have five joints. 



5. The ventral surface is pierced by three openings, the first 

 formed anteriorly by the overhanging of the dorsal surface and 

 posteriorly by a deep indentation of the sternal plate ; through 

 this opening the palpi and organs of the mouth are protruded (or 

 withdrawn at will), and in most species the orifice can be almost 

 entirely closed by the labium. The second orifice is rhomboidal 

 or oval, and is always closed by two chitinous plates like folding 

 doors, which open to afibrd a passage to the reproductive organs. 

 The third orifice is the anal, and is similar in shape to the genital, 

 and is closed by similar plates, which are usually larger than the 

 genital ones. 



6. There never are any visible eyes. 



Bihliograpluj. 



I have not attempted to give an exhaustive bibliography, but 

 only referred to the few authors whose works are of importance, 

 and a reference to which is almost necessary for the latter part of 

 this paper ; these I have arranged, not in order of date, but, to some 

 extent, in order of importance. 



The first place must be assigned to Nicolet's monograph of the 

 Oribatidae in the neighbourhood of Paris,* an admirable work, 

 beautifully illustrated, clear, and distinct. I have followed his 

 arrangement, introducing such species as Nicolet did not find, in 

 what appear to me to be their respective proper places ; but, while 

 doing so, I may say that I probably might not quite adhere to this 

 system were I myself writing a monograph, as, although it has 

 the advantage of great distinctness, it seems to me highly artificial, 

 and I doubt if one or two of the distinctions can be supported, for 

 instance, the great stress laid on the difference between homodactyl 

 and heterodactyl claws ; I doubt whether any truly homodactyl 

 claws exist in the family, it seems to me probably more a question 

 of degree. 



C. L. Koch, in his great work, f has described and figured an 

 immense number of species and given their classification in a sub- 

 sequent work ; % these two books form a vast storehouse of know- 

 ledge relative to the Acarina, and a monument of human industry ; 

 they are an absolute necessity to the apterologist, but it must be 



* ' Archives du Museum,' 1855, t. 7. 



t ' Deutscbland's Crustaceen,' &c. 



j ' Uebersicht des Arachuidensystems.' 



