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This means that not only the heavily chitinized structures normally 

 shown in such drawings are treated as opaque, but also the thin mem- 

 brane which closes the twelfth segment and reaches the anal opening. 

 X'isible through the various parts are a number of structures, of which 

 we represent only the hidden portion of the oedeagus and the long 

 hair-tuft on the claspers, when present. The latter is represented 

 by fine broken lines, and its point of attachment by heavy dots. The 

 outlines indicated by heavy lines are mostly definite, free margins. 

 We have departed from this usage in a few cases to show heavy areas 

 of chitin which are conspicuous and distinctive, as in Ada'ma amhrosiae 

 Murt. The claspers in this family are often thin, more or less inflated 

 sacs, which become flattened in mounting and exhibit two outlines of 

 approximately the same shape, the inner representing the actual inner 

 surface of the clasper. The harpe is developed only on the left valve, 

 and is usually rather simple. Near its base, and often embracing it, 

 the lower margin of the valve is often folded, forming, apparently, the 

 sacculus of Pierce's works. On the right valve there is frequently 

 a slight ridge which is probably a rudiment of the harpe. In Oidae- 

 matophonis mizar B. & L. this bears a small transverse lobe which 

 may be the ampulla of Pierce. In the thin membrane which connects 

 the bases of the valves and closes the twelfth segment there is devel- 

 oped an area of chitinization which becomes thicker as it approaches 

 the opening through which the oedeagus projects, and forms a free, 

 forked organ of n:ore or less complex shape which embraces this 

 opening. This structure appears to be homologous with the juxta of 

 Pierce. Its connections are not clear to us, but it extends very defin- 

 itely, decreasing in strength, in most of our slides toward the ventral 

 extremity, and exhibits definite lateral margins which we represent 

 by heavy lines, although they are continuous with the membrane men- 

 tioned. A few slides show what appears to be a ruptured connection 

 between the base of the fork and the inner face of the valves. Such 

 apparent connections are indicated by dotted lines. In Plafyptilia the 

 juxta is not so developed, but the oedeagus projects through an open- 

 ing in the posterior membrane whose sides are produced more or less 

 as slender lobes. The oedeagus has a ventral process near its base 

 by which it appears to be attached near the base of this opening. It 

 probably moves in an arc whose center is this attachment. The 

 gnathos is apparently not chitinized ; other structures require no re- 

 marks. We are at a loss to explain the remarkable development of 



