NEW OR LITTLE-KNOWN ACARI. 373 



and genera] appearance, it seems probable that the genera 

 Psorergates and Demodex are related to one another. 



Speleorchestes ventriosus, sp. n. 



§ . This new saltatorial mite differs from S. podicroides, mihi 

 in being much stouter in appearance ; the abdomen is especially 

 wide (hence the specific name ventriosus), being much stouter 

 than in S. poduroides. Ovipositor when protruded provided with 

 a basal collar-like structure or sheath as in S. poduroides, but it 

 is longer than in that species, its length exceeding the distal part 

 of the ovipositor that projects beyond it (whereas in S '. poduroides 

 the collar is much shorter than the part of the ovipositor that 

 projects beyond it). Shape of hairs and their distribution much 

 as in S. poduroides. 



Owing to its rather squat appearance, this new species of 

 Speleorchestes somewhat resembles Nanorchestes, but the anterior 

 part of the cephalothorax is quite separate and distinct from the 

 posterior portion, not being enclosed by it laterally ; posterior 

 part of cephalothorax much narrower than the abdomen and 

 divided from it by a distinct constriction (whilst in Nanorchestes 

 the posterior part of the cephalothorax is almost as wide as the 

 abdomen and only separated from it by a slight groove). 



Length (including chelicera?) 317 p. ; width of anterior (cephalic) 

 part of cephalothorax 62-67 fi • width of posterior (thoracic) part 

 of cephalothorax 107-1 10 [x ; width of abdomen 155-160 ja. 



Habitat. Hind head, Surrey ; a number of specimens collected 

 by the author under stones near the path running above the 

 natural hollow known as " the Devil's Punch Bowl " (just 

 below Hindhead Beacon), May 1918. 



Speleorchestes poduroides Hirst. 



I have added a few more measurements for comparison with 

 those of S. ventriosus, sp. n. 



Length (including chelicera?) 278-290 /j- ; width of anterior 

 (cephalic) part of cephalothorax 58-60 p ; width of posterior 

 (thoracic) part of cephalothorax 82-85 p ; width of abdomen 106- 

 115ju. 



Key to British Species of Saltatorial Mites (Genera Nanorchestes 

 and Speleorchestes). 



Body short and wide ; anterior part of cephalothorax en- 

 closed laterally by the posterior part Nanorchestes Tops. 



& Trouess. 

 Dorsal hair on chelicera slender and divided into two 



plumose branches N. coll inns Hirst 



(Mendip Hills). 

 Dorsal hair on chelicera rather short, stiff, rod-like, and 



not divided N. amphihius Tops. 



& Trouess. 

 (Littoral specie--.. I 

 Body more elongated ; anterior part of cephalothorax 



free (not enclosed laterally by posterior part) Speleorchestes Trgdh. 



