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ON TWO NEW PAEASITIC ACARI OF THE GENUS 

 LEIOGNATHUS, CN. (GAMASIDAE). 



By S. Hirst. 



{Published by permission of the Trustees of the British Museum.) 



Most of the species of Leiognathus are parasitic on small mammals (bats, 

 rodents, etc.), others occur on birds and a few also on reptiles. A number of 

 the species of this genus have been described under the name /liponyssus, but 

 personally I do not think that Liponyssus setosus, Kolenati (the type and first 

 described species of the genus Liponyssus) falls into the same natural genus as 

 the species described by recent authors under that generic name or under the 

 name Leiognathus. On the other hand, Kolenati's genera Ischoronyssus, 

 Macronyssus, Lepronyssus, Steatonyssus and Pimelonyssus certainly seem to me to 

 be congeneric with Leiognathus, Cn., and ultimately one of these names will have 

 to replace Canestrini's. 



Leiognathus creightoni, sp. nov. (fig. l). 



Q . Body elongate oval in shape ; some distance in front of the middle it is 

 slightly constricted, the part of the body posterior to this constriction being- 

 wider than the front part of it. The setae at the posterior end of the body are 

 rather long. Scutum (dorsal plate) large and rather wide, but it leaves a 

 considerable portion of the dorsal surface uncovered, especially at the posterior 

 end of the body (for its shape see fig. 1). A faint transverse line runs across 

 the scutum near the middle and it is possible, therefore, that it consists of two 

 practically fused shields in this species. A number of setae of moderate length 

 are present on its surface, eleven of them being arranged in a longitudinal series 

 on each side of it and these lateral setae have rather large sockets. Ventral 

 surface : sternal plate large ; it is wider than long and bears three pairs of 

 bristles. Immediately behind the genital operculum, there is a rather weakly 

 chitinised plate, which has a short seta on each side of it ; the posterior end of 

 this plate is not angular but rounded off. Anal plate pear-shaped, its posterior 

 end being pointed and finely striated ; the three usual setae are present on its 

 surface. Peritreme rather short, for its anterior end is situated nearly opposite 

 (slightly in front of) the coxa of the third leg. Chelicerae long ; their digits 

 long, slender and apparently without any teeth on their edges. Legs 4, 1, 3, 2 ; 

 second and third legs considerably shorter than the others. First leg stout, the 

 other legs more slender. Dorsal surface of anterior legs furnished with several 

 long setae. Coxa of first leg armed with a conical spur on the inner side below. 

 Coxa of second leg with a very large hook-shaped spur on its posterior side 

 below and this spur bears a large tooth ; on its anterior surface the second coxa 

 has a dorsal spur, which points forwards. Third coxa with two conical spurs on 

 its posterior surface. Fourth coxa with a single posterior spur. The first leg 

 has also a number of short but stout teeth or spinules on its ventral surface ; 



