20 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
genitalis; a posterior, represented by the flattened surface of the 
quadrant; and a dorsal, the portion extending from the upper end of 
the flattened surface to the anterior margin. From its ventral surface, 
as thus designated, depends the penis (PI. 6, fig. 40, p.) and its paired 
accessory structures. \Vhat is here termed the penis is actually the 
penis sheath. The downwardly directed forceps (PI. 6, fig. 40, /.) is 
attached to the junction of the ventral and posterior surfaces. It 
consists of two paired hollowed prongs (PI. 5, fig. 30; PL 6, fig. 37, 
fpg.) each of which is divisible into a swollen, hairy, proximal portion, 
and a smaller, somewhat claw-like, darkened, distal part. The latter 
is naked and the tip curves downward and slightly inward. The 
prongs are so attached at their base that they spread apart and while 
the tips are convergent, they do not meet. The appearance of the 
forceps is characteristic for all species of Ravinia except that in one the 
tips do not converge. The 'base of the forceps,' used in descriptions 
does not refer to any definitely prescribed area, but merely means the 
basal part ol the prongs. In this species (also genus) it should be 
noted that the base of the forceps bears no upward flap-like extensions 
that in other genera partially overlie the anal area. The base of each 
prong may be bluntly pointed but together they present a sort of 
rounded appearance. 
On the posterior surface of this segment just above the base of the 
forceps is a small, irregularly triangular, membranous space, the anal 
area (PI. 6, fig. 39, a.) through which the anus opens. Extending 
upward from the apex of the triangle is an impressed line in the chitin 
(PI. 6, fig. 39, ial.), sometimes indistinct, but always present. 
Lying in the membrane at each side below the anterior base of the 
forceps, and between it and the lateral, posterior, ventral edge of the 
notum, is a small somewhat triangular sclerite, the accessory plate 
(PI. 5, fig. 30; PI. 6, figs. 37, 40, ac; paralobes, Pandelle; Neben- 
lappen, Bottcher). 
Observing the ventral side of the segment, the anterior corners of 
the notum are seen to be prolonged into medially projecting processes. 
These articulate with the sides of a somewhat swollen U- or A -shaped 
plate, apparently the progenital sternum of LoAvne. It will be here 
termed the genital sternum. The anterior third of this plate is 
solidly filled in and may be conveniently called the base. From the 
posterior sides of the latter arise the arms. Part of the base lies within 
the cavity of the seventh segment concealed by overlying membrane. 
