CYDNIDAE OF THE WESTERN HEMISPHERE — FROESCHNER 349 



study than could be undertaken at the present time. Laterally in 

 the spiracular area of sternites III to VII there occurs a pair of 

 sensory hairs or trichobothria. Just what it is that the hairs "sense" 

 appears controversial. When Hansen (1917, p. 258) reviewed and 

 discussed the subject of external sensory hairs he concluded, "But 

 I think I have shown with tolerable certainty that the trichobothria 

 in terrestrial Arthropods are scarcely auditory organs but tactile 

 hairs of special structure." Tullgren's (1918) study of the tricho- 

 bothria on Hemiptera contained illustrations of them and resulted 

 in some interesting speculations on their role in the higher classi- 

 fication within the order. His conclusions on the Cydnidae were 

 based on an unfortunate choice of two genera of the subfamily 

 Sehirinae; all members of that subfamily agree with the Pentatomidae 

 proper in having two trichobothria arranged in a transverse row 

 behind each spiracle. If he had chosen genera of any other subfamily 

 he would have realized that other patterns also existed in the family. 

 In fact, the present study recognizes four additional arrangements, 

 making it possible to establish five subfamilies on the basis of the 

 trichobothrial arrangements in both the nymphs and the adults. 

 These categories can be supported by additional features derived 

 from other parts of the body. For further information on such use 

 of the trichobothria the reader is referred to the discussion under 

 the family heading. 



Measurements were taken in a standard manner. Width and 

 length of head, transverse ocellar width, and size of space separating 

 eye and oceUus were taken from a dorsal view of the head which 

 placed the greatest expanse of outline at right angles to the line of 

 vision; the greatest length of antennal and labial segments was 

 taken from side view; the pronotum was held so that a plane through 

 the margins was at right angles to the viewer and the length was 

 measured along the midline and the width across the humeri; the 

 scutellum likewise was held at right angles to the line of vision and 

 the length was taken along the midline from the bottom of the basal 

 transverse impression to the apex, and the width was measured 

 basally with the lateral ends of the curved basal impression forming 

 the points of limit. The total length of the insect is that of the 

 body alone, the position of the membrane being too variable to give 

 a fixed point for measuring; but even the "length of body" is not as 

 accurate as might be desired because the position of the head often 

 varied from specimen to specimen. All measurements are given in 

 milHmeters. 



The term alutaceous does not appear to have common usage in 

 hemipterology but is very helpful in describing the surface micro- 

 sculpture of some of these insects. When a surface is alutaceous 



