20 Studies on Arthropoda. I. 



ORDER RICINULEI 



The main paper on this small but most interesting order is: 

 H. J. Hansen and W . Sorcnscn: On Two Orders uf Arachnida. 

 Opiliones, especially the suborder Cyphophthalmi, and Rici- 

 nulei, namely the famil>- Crj^tostemmatoida^. Cambridge. 

 At the l^niversity Press. 1904 (4to). — Since its publication 

 nothing, as far as I know, has been added to our knowledge 

 of the recent forms. But a curious attempt by Prof. Fr. Dahl 

 (Berlin) may be briefly mentioned. In 191 1 he published a 

 small treatise: Die Horhaare (Trichobothrien) und das System 

 der Spinnentiere (Zool. Anzeiger \'ol. XXXVII, p. 522 — 532). 

 He ascribes a high systematic value to the exi.stence and distri- 

 bution or non-existence in the various orders of Arachnida of 

 that kind of sensor}' hairs which he names "auditory hairs" ; 

 besides, without an}' real discussion and without pointing out 

 any feature hitherto overlooked in the orders Pedipalpi, Pal- 

 pigradi, Ricinulei, Opiliones, and Acari, he refers the Palpi- 

 gradi to the Pedipalpi, the Ricinulei to the Opiliones, and the 

 suborder Cyphophthalmi from the Opiliones to the Acari. That 

 such classification is only of the retrograde kind is rather evi- 

 dent; it is scarcely necessary to prove its futility Ijy detailed 

 enumerations of structural features and a lengthy discussion 

 of their relative value in the orders and suborders in question. 

 In a paper published in igi/'^). I have dealt with the so-called 

 "auditory hairs" in Arachnida and in the two other classes of 

 terrestrial Arthropoda. — On the palaeozoic forms of the order 

 Ricinulei important contributions have been published by 



') H. J. Hansen. On the Trichobothria ("auditory hairs") in Arachnida, 

 •Myriopoda, and Insecta, with a summary of the external sen.sory organs 

 in Arachnida (Entomologisk Tidskrift utg. av I-.ntoinol iMirenineen i 

 Stockhohii. Arg. 38, xgiy, p. 240 — 259. 



