347 



Abdomen never witli a cliitin- Aljdonicn sonietiini's with a 



ous hood-like projection from its chitinous hood-like projection 



anterior margin. from its anterior margin. 



Olaws of legs usually small and Claws of legs always stout; if 



monodactyle ; if tridactyle the tridactyle the dactylcs are sub- 



dactyles are usually unecpial. equal. 



When we consider all these points of difference, it appears 

 to us that they are not only of sufficient importance for the 

 separation of the tvyo forms into different families, but that 

 they might even justify a wider separation and a higher rank. 

 About the only important characters the two have in common 

 are the chitinous integument and the presence of the pseudo- 

 stigmata and tlie pseudostigmatic organs. Mr. Baidvs, in his 

 treatise on "The Acarina, or Mites" (,Proc. V. 8. Nat. Mus., 

 Vol. XXVIII., p. 1-114), separates those forms which have the 

 cephalothorax hinged to the abdomen from the otlier oril)atids, 

 under the family name of HoplodciDiidir. This separation 

 and name the author of this paper lias adopted. 



Mr. Michael's separation of those forms wliicli possess ab- 

 dominal wings from those which do not {"A/ifr/-()</iisfcn'(t") we 

 accept, raising both forms, howevei-, to family rank, and gi\ ing 

 the first-mentioned the old name ()rHiiiii(hi\ since it contains 

 the old genus Ori/iafd. This division is not altogether happy 

 fortworeasons: hrst, many authors may consider thesnnill, shelf- 

 like chitinous expansions from the shoulders of the abdomen 

 in tlie case of some genera (as Xof(i>tj)/s and 7\-(/i'()cr<niii.s) as 

 homologous with the true abdominal wings, or pteroniorphie; 

 second, there are not many other fundamental characters in 

 support of the division. Notwithstanding these facts, we con- 

 sider the development of abdominal wings — especially when 

 takinginto account their defensive value and the hal)its of mites 

 possessing them, and some other points of difl'erence as well — 

 as of sufficient importance to entitle such forms to family rank. 



Since we have applied the family name Orihatidd- to those 

 forms having abdominal wings, the remaining forms, the ''Ap- 

 ten>(jfisf('ir(/', we naturally consider as constituting a family, us- 



