24 IOWA STUDIES IN NATURAL HISTORY 
Concealed genital organs: The genital chamber! of the male has what 
appears to be a rather complete and fully chitinized armature, consisting 
of various plates, spines and projections. The sinistral hook, fig. 1, a, is a 
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rather slender projection with the basal half broadly flattened vertically, 
thence but slightly flattened and gradually tapered to a more flattened, 
apically incurved and briefly fureate tip; this hook very likely projects 
somewhat, the tip not being wholly concealed within the chamber. Partly 
overlying the sinistral hook basally is a laterally broadly flattened pro- 
jection, gently twisted inwards, the outer surface convex and the inner 
surface concave and the upper apical margin prolonged and narrowed to 
form a sharp, slender spine extending to about the apex of the sinistral 
hook; this organ is illustrated at Fig. 1b. To the right of the last noted 
organ, and at about the middle of its length, is a thick subquadrate apically 
1. The taxonomic importance of the concealed genital organs of roaches, especially of 
the males, is becoming more appreciated, and the use of such characters has been 
encouraged by the recent studies of Mr. Hebard, who has introduced a few special 
terms for certain of these organs. The three following are now in use, and their 
significance is as follows: 
Genital chamber. The space between the subgenital and supraanal plates in which 
are contained the concealed genital organs. By cutting transversely along the base 
of the subgenital plate with a sharp scalpel or fine pointed scissors, that plate may 
be, in fresh or alcoholic speciments, laid over sideways, preferably to the right, or 
the left as the roach lies on the back; the incision at the base of the plate is not 
made quite across the entire width, thus leaving a small portion to act as a hinge 
when it is laid over. 
Sinistral genital hook. A more or less slender, often incurved, organ projecting 
more or less conspicuously on the left side of the genital chamber of the male, usually 
wholly concealed before the subgenital plate is laid over, but sometimes projecting 
somewhat beyond that plate. There is much variation in the shape of this hook, as 
will be seen by the figure 1 of the present report and figures on plate ix of Hebard’s 
work on the United States Blattide in Mem. Amer. Ent. Soc., No. 2. 
Dextral genital hook. A usually more or less thickened broad plate lying in the 
right side of the genital chamber of the male, also variable in shape. Illustrations 
of those of Arenivaga sps. will be found on the above mentioned plate by Hebard. 
Some roaches, the new Eurycotis here described being a good example, have various 
other very remarkable chitinized spines, spurs, plates, etc., and eventually a number 
of various terms will be necessary for their proper designation. More extensive com- 
