346 THE AMERICAN MONTHLY [Nov., 



d Meso-thorax separated from Meta-thorax by a 



suture. Trinoton 



dd Meso-thorax united to Meta- thorax without suture- 



Laemabothrium 



aa No orbital sinus or if present shallow or covered by an expansion 



of upper, part of head. 



b Sides of head straight or a little concave. Forehead with two 



palettes. Physostomum 



bb The sides of the head sinuous without palettes. 



c Body very broad. Meta-thorax shorter than pro-thorax. 



Eureum* 



CO Body elongate. Prothorax shorter than meso-thorax and 



meta-thorax together. 



d Orbital sinus occupied by a strong swelling, the 



bands of the sternum forming a quadrilatera 



without median spots. Nitzschia 



dd Orbital sinus without swelling, slightly indicated 



or wanting entirely. Sternum with median 



spots. Menopon 



A A Tarsus with a single claw, (infesting guinea pig). Gyropus 



*Not yet recorded for North America. 



To Mount Certain Salts. 



By NO SIG. 



PARIS. 

 DI-ACETATE OF COLDER. 



Di-acetate of copper is a very good example of a di- 

 chroic crystal. It shows a strong blue color in one 

 direction and a bright green in the other. To see this 

 effect, it is only necessary to use the polarizer, the ana- 

 lytic effect of the salt supplying the place of the analy- 

 ser. 



This salt should be allowed to evaporate spontaneously, 

 and the slide must be thoroughly dried before the salt is 

 mounted. 



The crystals will stand the heat of the hot plate with- 

 out any danger of their being spoiled ; so that they 

 could be mounted in balsam with great facility, but un- 

 fortunately when mounted in balsam, although the crys- 

 als are pretty distinct, they are surrounded with a halo 



