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note in this image the lack of an orange mark between eye and wings. an accompanying graphic of the same male shows the narrow and well-defined orange bands across ventral abdomen and distinct form of posterior abdomen. these, as noted at an excellent web site regarding cicadas, http://insects.ummz.lsa.umich.edu/fauna/Michigan_Cicadas/Periodical/Index.html
yield a male septendecula.

my personal observation of septendecula and septendecim posit the absence or presence of the orange mark as the distinguishing characteristic. in some septendecim the mark is quite small and pale, and consequently not easily observed.

i have seen septendecula as large as septendecim, and male septendecim with orange ventral stripes as narrow and well defined as septendecula, while others have broader bands and a u-shaped orange mark with the top at the initial ventral segment and the bottom at the distal side of the abdomen.
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imageminder