2O Studies on Arthropoda. I. 



ORDER RICINULEl 



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

 H. J. Hansen and W. Sorensen: On Two Orders af Arachnida. 

 Opiliones, especially the suborder Cyphophthalmi, and Rici- 

 nulei, namely the family Cryptostemmatoida?. Cambridge. 

 At the University 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 1911 he published a 

 small treatise: Die Horhaare (Trichobothrien) und das System 

 der Spinnentiere (Zool. Anzeiger Vol. XXXVII, p. 522 532). 

 He ascribes a high systematic value to the existence and distri- 

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

 that kind of sensory hairs which he names "auditory hairs" ; 

 besides, without any 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 by 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 I9I7 1 ). 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 



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

 Myriopoda, and Insecta, with a summary of the external sensory organs 

 in Arachnida (Entomologisk Tidskrift utg. av Entomol. Foreningeii i 

 Stockholm. Arg. 38, 1917, p. 240 259. 



