NO. II NAIADS OF DRAGONFLY GENUS PLATHEMIS—LEVINE 21 
ABDOMINAL STERNA 
The sterna (fig. 21) are slightly convex and each of the first nine 
is divided by two longitudinal sutures into “a broad median plate (ms) 
and two small lateral plates (Is), which latter are movably hinged on 
the edges of the tergum and on the median sternal plate” (Snodgrass, 
1954). The sternum of segment Io is undivided and unseparated from 
the tergal surface. 
The MEDIAN PLATES (ms) or median sternites (Snodgrass, 1954) 
of abdominal segments 1 and 4-8 of the male and of segments 1-8 in 
the female are unmodified and devoid of genital processes. The sec- 
ond and third median sternites of the male bear rudiments of the ac- 
cessory genitalia (gn) of the adult, and the ninth median sternite 
bears the centrally located rudimentary genital pore (gp). On the 
ninth median sternite of the female there are two small, centrally 
located tubercles (va), which are most probably the rudiments of the 
valvulae of the ovipositor. 
The LATERAL PLATES (ls) of the first eight segments bear the ab- 
dominal spiracles (sp), the largest of which is on segment eight. 
Numerous authors, including Calvert (1893), Wallengren (1914), 
Tillyard (1917), and Whedon (1918), have referred to the lateral 
plates as “pleurites,” but Snodgrass (1954) states that the term 
“pleuron” “has no very definite meaning as applied to the abdomen.” 
He substitutes instead the term “laterosternites” for the lateral sternal 
plates. In Plathemts lydia each laterosternite of segments 3, 4, and 5 
is secondarily divided into a small anterolateral sclerite (episternite— 
Wallengren, 1914; triangular sclerite—Schmidt, 1951) and a larger 
posterior sclerite (epimerite—Wallengren; spiracular sclerite— 
Schmidt) which bears the spiracle. 
Numerous posteriorly directed, short, spiniform setae are borne on 
the lateral keels, the lateroposterior margins of laterosternites 2-9, 
and the posterior margins of median sternites 7-9. Numerous other 
minute spines and setae are present on the entire ventral surface and 
are generally larger on the laterosternites than on the median sternites. 
ANAL APPENDAGES 
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The anal appendages (figs. 22, 23) of the nymphal abdomen are of 
: interest because of the different interpretations of their homologies. 
These terminal structures may be divided into two groups on the 
_ basis of their segmental relationships. The first group consists of 
epiproct, paraprocts, and cerci, of which the first two are thought to 
comprise the modified eleventh abdominal segment (Heymons, 1904) 
