HYDRACHNID^ IN ' ACARIDES OF BERWICKSHIRE ' 27 



nidae or water-mites. Apart from any interest attaching 

 to the species themselves, the record is interesting as it 

 constitutes, so far as I know, the earliest British record 

 of Hydrachnids. 



Dr. Johnston describes these three species under the 

 names of Hydrachna cruenta Miill., Atax histrionicus^ and 

 Hydrachna nazca, the last being a new species. A con- 

 sideration of Dr. Johnston's descriptions leads me to the 

 conclusion that 



Hydrachna cruenta Miill. Qohnston) =iDzplodontus despiciens 



(Miill.). 

 Atax histrionicus = Livinesia histrionica (Herm.). 



Hydrachna Jidica Johnston = Hygrobates reticidatus (P. Kram.). 



= Hygrobates na'icus (Johnston). 



DiPLODONTUS DESPICIENS {MutL). 



Johnston described what he believed to be Hydrachna cruenta 

 Miill., but his description of the eyes points not to the genus 

 Hydrachna, in which the two lateral eyes are fused together and 

 enclosed in a capsule, but to Diplodontus, in which the two lateral 

 eyes are separated one behind the other, and are situated on the 

 body margin, where, owing to bulging of the body, they are at 

 times seen with some difficulty. 



In describing the palpi as four-jointed, Johnston evidently 

 considered the fifth segment as a claw, which, in this case, is 

 opposed to a pointed elongation of the fourth segment so as to 

 form a chela-like termination to the palpus. 



LiMNESiA HISTRIONICA {Herm.). 



I do not see any reason to doubt that the species described by 

 Johnston as Atax histrionicus Duges is any other than Linmesia 

 histriojtica Herm., although the length of the palpus as compared 

 with that of the body is rather shorter than usual. 



Hygrobates naicus {Johnston). 



SYN. 



1848. Hydrachna ;?«/f«, Johnston. "History of the Berwickshire 



Naturalists' Club," vol. ii. p. 314. 

 1879. Nescea reticulata^ Kramer. " Archiv fiir naturgeschichte," 



vol. i. p. II. 

 1 88 1. Hygrobates gracilis^ Haller. " Mittheilungen der Bern, natur- 



forschenden Gesellschaft," Heft ii. p. 68. 



