464 SUMMARY OF CUERENT RESEARCHES RELATING TO 



situated near to or just below the average high-water mark, where they 

 were liable to complete submergence at spring tides." Rattray found 

 that while many of the retreats were often merely drenched by spray, 

 numerous small retreats occupied by immature specimens occurred 

 amongst the wet seaweed exposed at low water, and must be sub- 

 merged every high tide. Two other species have been previously re- 

 corded from sea-shore rocks — A. maritima 0. P. Cambr., from Otago, 

 and 0. piscator Hogg, from the Campbell Islands. The African form is 

 very near A. piscator. Perhaps the genus is widely distributed in the 

 southern hemisphere ; perhaps distribution is. aided by wind, perhaps by 

 floating seaweed. • 



Water-mites.* — William Williamson gives a useful account of the 

 general characters of Hydracarina, and describes in detail Thyas venustra, 

 a type of the LimnocharidEe, and Limnesia fidgida, a type of the Hygro- 

 batidffi. The two families are contrasted, and a key is given to five 

 Scottish species of Limnesia. A short account is given of the life-history 

 of water-mites. The eggs are usually laid in anchoring and protective 

 gelatinous masses. The hexapod larva that emerges seeks an aquatic 

 insect, to which it attaches itself by its relatively strong palpi. It is 

 very doubtful if the larva is really parasitic at all, as shortly after attach- 

 ment the limbs drop off and the larval body begins to swell out owing 

 to the development of the nymphal body within. When mature the skin 

 is ruptured, and the eight-legged nymph emerges. The host is of 

 necessity some insect which either inhabits or spends part of its existence 

 near the surface of water. Consequently, during the transition from 

 larva to nymph, the mite exists for considerable intervals — i.e. during the 

 flight of insects — out of the water, and in this way in many cases the 

 dispersal of species may be accounted for. Nymphs may readily be 

 distinguished from adults by the presence of what has been termed a 

 provisional genital area. 



Occurrence of Pseudo-parasitic Mite on Cat.f — Stanley Hirst 

 reports from a cat infected with mange the mite known as CheUtiella 

 parasitivorax Megnin, which normally lives in the fur of the rabbit and 

 hare, and is said to feed on the minute Acari {Listrophorus, etc.) found 

 on these rodents. Presumably in the case of the cat it fed on Notmdrus 

 cati, which causes the mange. This species of CheUtiella can be readily 

 distinguished from the others by the absence of the claws, which have 

 entirely disappeared. A careful figure is given. 



New Water-mites. I — Chas. D. Soar describes Dartia harrisig. et sp.n., 

 from Dartmoor. The body is oval in outline, the skin soft, the eyes 

 wide apart near the margin of the body ; the legs without swimming- 

 hairs, the fourth pair of legs without claws ; the epimera in four groups ; 

 the genital area like that of Lilertia, but with four acetabula (not the 



* Scottish Nat., No. 62 (1917) pp. 37-47 (6 figs.). 



t Ann. Mag. Nat. Hist., xx. (1917) pp. 132-3 (1 fig.). 



i Jouru. Quekett Micr. Club, xiii. (1917) pp. 1-6 (2 pis.). 



