960 " FA^iiLv L. — s('.\i;ai'..i;[T)/E. 



or with wliicli they are found in e()iii!)any. The two sexes may be 

 distinguished l)y tlie nude lieing the h'ss rol)nst, less widened be- 

 hind and less convex ; and in our species by having the antennae 

 usually longer and the clul) distinctly longer than in the female, 

 except in crenulata and alhina. In most males the abdomen is more 

 or less flattened and the last two ventral segments are more or less 

 modified, the next to the last often bearing a transverse "ventral 

 ridge," and the last segment a hollow depression or concavity. 



The sexual organs have been shown l)y Smith (Proc. U. S. Nat. 

 ^lus., loc. oil.) to possess a certain and unvariable form in each 

 species, and in the future they will doubtless be largely relied upon 

 to furnish distinguishing characters. In fresh or relaxed speci- 

 mens they can be easily pressed out by squeezing the abdomen, or 

 removed by a pair of forceps. The name "clasper" has been given 

 to the horn-like organ whose variations form the specific differences 

 in the male, while those of the female consist of a pair of broad 

 "inferior plates." above which are a pair of "superior plates," 

 generally smaller, narrower and much more variable than those 

 below. When the (M^gans are most fully developed the superior 

 plates are notched at their point of union and are surmounted by a 

 "pul)ic process" very variable in shape in the species and there- 

 fore furnishing important distinguishing characters. In the fig- 

 ures of these sexual organs in the plates which follow, the letters 

 througliout have the same meaning, viz. : a. claspers of male from 

 front or above; J), right clasper; c, left clasper; d, female organs; 

 (', ventral characters of male. These are always sublettered as fol- 

 lows: i, inferior plates; .v, superior plates; p, pubic process. 



The sjiurs of the liind tibia^ of the males are also much used in 

 classification. In one division the two spurs are both free or mov- 

 able, being united to the til)ia' by a iiKMubranous hinge, and usually 

 inclined at an angle, as they are in all females. In the other and 

 larger division the inner spur is a fixed prolongation or part of the 

 edge of the til)ia^ itself. A little practice will soon enable the be- 

 ginner to readily see the rigidity or fixedness of the inner spiu', 

 without attempting to move it. 



IMuch care must be taken in counting the joints of the antenna^ 

 which ai'e (either nine oi' ten in uumher. The club is always com- 

 ])()scd of three elongate joints, resting at riglit angles to the others. 

 (Fig. 4, No. If).) Joint 7 or H, as the case may be, is very thin, 

 triangular in foi-m and closely apju-essed against the base of the 

 inner joint of the club, and is therei'ore liable to be overlooked. 



