966 FRESH-WATER BIOLOGY 



trays. For these a standard size should be adopted, so that they 

 will conveniently fit into the drawers of the cabinet. In the 

 National Museum at Washington, the unit is i by 2 inches, and 

 the larger sizes are all multiples of that unit. In the Academy of 

 Natural Sciences at Philadelphia, the unit is ij by 3. There is 

 one advantage in the use of the larger unit where space is a serious 

 question. For the small species the vials may be used only ij 

 inches in length, and two vials can be put into one tray, thus dou- 

 bling the capacity of the drawer. The trays should be of the same 

 depth. One-half inch is sufficient for most of the univalve species. 

 For the larger species, such as the Unionidae, requiring trays of 

 good size, f inch is better. These trays can be had of any paper- 

 box manufacturer, or can be easily cut out of cardboard by the 

 collector, the corners being fastened together by strips of gummed 

 paper. The character of the cases for a collection is determined 

 by the means and inclination of the collector. Any case of shallow 

 drawers will do. If, however, cases are to be made, they should 

 be made of a standard size with interchangeable drawers. Each 

 tray should have a neat label giving the serial number, the name, 

 and the locality of the specimens it contains. A box, bottom 

 side up, can be used for separating the genera and species in every 

 drawer. Small labels of convenient size for designating them can 

 be had, already gummed, at any bookseller's. 



In packing shells, small specimens should not be mixed with 

 large ones, as they are apt to get lost; nor should fragile shells be 

 put in with stronger ones, as they are likely to be broken. The 

 minute specimens can be put into gelatin capsules, small vials, 

 quills, or paper tubes made by rolling writing paper around a lead 

 pencil, gumming down the edge and stopping the ends with cotton. 

 Do not mix shells from different localities. Write the locality on 

 a label and wrap it up with each vial or package. Use plenty of 

 cotton in packing fragile shells. Pill boxes and match boxes are 

 convenient for packing purposes. Wrap up each vial or box sepa- 

 rately, then, if a smash does occur, there is a fair chance of saving 

 some of the specimens and no danger of mixing the contents of 

 different packages. Do not send paper boxes by mail. Pack in 

 a wooden box. 



