Book-lice and Bark-lice; Biting Bird-lice 113 



3. Discoidal rcU closed M yopsocus. 



Discoidal cell open Elipsocus. 



4. Discoidal cell closed 5. 



Discoidal cell open 6. 



5. Discoidal cell four-sided. Psocus. 

 Discoidal cell five-sided. 



.Xmphigerontia. 



6. Third posterior cell elliptical. 



C.ECILIUS. 

 Third posterior cell elongated. 



POLYPSOCUS ^"'^ '4^' — Diagram of venation of a Psocid. 

 _, . , , . 11 u . d, discoidal cell; la, 2a, w, posterior cells. 



Third posterior cell absent. ^^^^^^ g^^^^^ 



Peripsocus. 

 The few North American species of the true book-lice or Atropidse are 

 included in five genera, which may be distinguished as follows: 



The technical terms, hitherto undefined, used in the following table are the following: 

 squaniw, wings in the condition of small scales or pads; hyaline, clear, not colored. 



1. MesG- and metathora.x united, no wings Atropos. 



Meso- and metathora.x separate, rudimentary wings 2. 



2. Wings with veins Doryptervx. 



Wings veinless, in form of squama or tubercles 3. 



3. Squamae small, hyaline Clothilla. 



Squamse in the form of scars Lepinotus. 



Small tubercles in the place of squamae Hyperetes. 



The genera .\tropos and Clothilla were named for two of the three Fates 

 of mythologVi and a third genus was named Lachesis for the third Fate, but 

 unfortunately the last genus was not a valid one, so the book-lice have lost 

 their third Fate, and by the rigid laws of zoological nomenclature can never 

 regain her! The few species of these two Fate-named genera are the com- 

 monest of the book-lice. Atropos divinatoria is the species usually 

 found in books. It is about i mm. long, is grayish-white, and the small 

 eyes show as distinct black specks on the head. It does not limit its feeding 

 to the paste of book-bindings, but does much damage to dried insects in 

 collections. To this insect has long been attributed the power of producing 

 a ticking noise known as the "death-watch," but McLachlan, an authority 

 on the Corrodentia, does not believe that this minute insect "with a body 

 so soft that the least touch annihilates it can in any way produce a noise 

 sensible to human ears." A small beetle, called Anobium, is well known 

 to make such a ticking (by knocking its head against the wood of door-casings, 

 floors, etc., in which it lives) and probably the "death-watch" is always 

 made by this beetle. 



Bird-collectors are often annoyed by small, wingless, flat-bodied, swift- 

 running insects which sometimes escape from the feathers of bird specimens 

 to the hands and arms of the collector. Poultry- raisers are sometimes more 

 seriously troubled by finding them so abundant on their fowls as to do con- 



