100 (dr. a. c. oudemans"). notes on acari. 



groups. Not long ago Piersig {Zoologica^ 1898) admitted a few 

 subfamilies. Why then has he abandoned them in a rigorously 

 systematic standardwork 7 Why has he separated the two salt- 

 water-genera from the fresh- water-ones , and has he not placed 

 them in the neighbourhood of the related fresh- water-genera ? 



The apparently oldest Hydrarachnïdae are the not switnming 

 LimnocJiar'mae (Piefisig's genus 1), which moreover are provided 

 with the crista of the thrombidiid progenitors, and which therefore 

 are considered as Thromhidiidae by Trouessart, unjustly in my 

 opinion. 



Then follow the related Eulaluae (Piersig's genus 2), in which 

 the crista is shortened so, that it has less length than breath. 



Then follow the remaining Hì/drarachiidae, in which the crista 

 has disappeared without leaving any trace. Of this natural group 

 Piersig's genei-a 4 — 16 aie provided with palps, of which the 4th free 

 joint dorsally and distaily is lengthened claw-like, so that the 5th joint 

 hangs on the ventral side of the 4th joint ; indeed a pi'imitive 

 character, typical that of 2'/^ro?MÔeV/iir/a^, their ancestors. — N". 6 — 16 

 of these genera have mandibles of two joints, a primitiv character; 

 of these two joints the second one is claw-like too. N''. 6 — 16 of 

 Piersig's genera are called the Hydryphantinae. 



They are followed in my opinion by Piersig's genera 4 and 5, 

 which possess mandibles of one joint, and this is stylet- shaped. 

 Both these characters are secundary. This little group is called 

 Hyd/i'araehninae. 



Now we are proceeded to the genera 3 and 17 — 55 of Piersig. 

 They have palps, of which the 4th joint is not lengthened dor" 

 sally and distaily claw-like, which consequently have lost this throm- 

 bidiid character. As to the genera 17 — 55, they form a natural 

 group : Hygrobatinae, 



As to genus 3, Piersigia, Piersig himself places it next to the 

 Eulainae. In my opinion unjusfly. it has abnoimal palps, some- 

 what resembling those of Liniiiocharinae, a consequence of conver- 

 gency (cf. Ixodinae). I should like to erect for this genus a subfamily 

 apart : Plersigilnae, at the end of the llydraraclmidae. 



