PREPARATION FOR STUDY 9 



When mounted dry, pselaphids fall into two groups. First, all "large" 

 species (1.5 to 4 mm. in length) should be mounted upon a stiff card triangle 

 of which the point is bent sharply for about a half millimeter (cf. Ross, 1934, 

 for general details). For the small species (1.5 to 0.6 mm.) the bent point of 

 the triangle is too broad. Such species should be mounted upon the point of an 

 unbent triangle or upon a bristle; in this case the specimen should not be 

 pushed into the mounting cement but allowed merely to adhere to the outer 

 convexity of the drop of cement. 



Such triangle mounting is best done under the dissecting binocular to in- 

 sure clean work. When mounted, the left side, both ends, and the dorsal and 

 ventral surfaces should be clean of cement and are easily studied with mag- 

 nifications up to 100 diameters. With experience, the binocular mounting is as 

 rapid as good mounting without the aid of the microscope, and is far more 

 clean and accurate. The mounting can be varied to allow this or that genus 

 to be set in such a way that the essential differential characters can be seen 

 at the greatest advantage, e.g. the ventral face of the tenth antennal segment 

 in one group, the anterior tarsi or mesocoxae in another, and so on. 



As to cementing fluid, either a good glue slightly thinned or Canada bal- 

 sam can be used, and the arrangement of the beetle on the triangle with the 

 cement is best done by specially ground needles. The tools I have found most 

 useful are a small paint brush with the hairs cut away save for a tuft of about 

 three or four bristles remaining; needles made from aluminum wire, sharpened 

 on emery-cloth under the binocular to give one straight needle and one sharply 

 bent needle, each with very slender shafts and as long and fine a point as 

 possible; a micro-dissection knife for genitalia, made by grinding a No. 1 

 insect pin on both sides near the point until a small, sharp blade is produced. 



Length or other dimensions can be best obtained by using a crosslined 

 reticule in an eye-piece of the binocular dissecting microscope; the fine squares 

 of the reticule should have a length and width of between a tenth and a four- 

 teenth of a millimeter. Drawing the entire or a part of the specimen can be 

 greatly facilitated by the use of the reticule. Thus if lightly ruled paper is 

 used, the part to be drawn, whether a wholemount or a microscope slide, can 

 be accurately transferred, square by square, to the paper, from the image 

 covered by the net of lines in the reticule. 



In the preparation of microscope slide mounts, which are essential for 

 many taxonomic studies, large pselaphids can be mounted in depression slides 

 or the cover glass held up by bits of glass or rubber; or the pselaphids can be 

 dissected and mounted in sections. 



The exact method of mounting on slides depends upon the use for which 

 they are intended. For most taxonomic purposes, the beetles are allowed to 

 remain in 95 per cent ethyl alcohol for twenty-four hours, cleared in cedar- 

 wood oil for twenty-four hours, and then mounted in Canada balsam. Such 

 slides can be examined with ease at 400 diameters magnification, and both 

 dorsal and ventral surfaces are at one's disposal by turning the slide over. In 

 order to do this the slides should be very thin, else the higher magnifications 



