508 Mr. D. Sharp and Mr. F. Muir on the Comparative 



" ring-piece," the cap (a) or lateral lobes forming a wide curved plate 

 slightly emarginate; the basal-piece forming a large shield-shaped 

 plate with a deep keel down the centre (6). Internal sac large, with 

 complex armature. 



Gorylophus cassiclioides is of the same type. At present 

 we cannot directly connect this to any other type ; the 

 small median foramen with the internal sac contained in 

 the median lobe is unique among the "ring" forms, where 

 it is the rule to have a large median foramen and the 

 internal sac passing through it, when not evaginated. 



Family SCYDMAENIDAE. 



Forms examined : Stenichnus coUaris Mlill., England. 

 Uumicnts (recently ScydmacmLs) tarsatus MiilL, England. 

 Leptomastax coquercU Fairm., Corfu. 



Figs. 56, 56a, & and c, 57 PI. LI. 



Stenichnus collaris (PI. LI figs. 56, 56'"/, o6h, 56c). 



The distal jiortion of the median lobe forms a short thick irregular 

 tube ; the basal part being curved under and prolonged into a flattened 

 narrow process (/), a band of membrane (m) connecting the two 

 portions ; the median orifice is large, at the distal end ; the median 

 foramen small, situate on the dorsal face about two-thirds down the 

 tubular distal end of the median lobe. Lateral lobes narrow flat pro- 

 cesses, attached to the median lobe at the dorsal edge of the median 

 foramen. Internal sac short but very complex (56c). On the dorsal 

 face there is a membranous surface bearing a pair of keels studded 

 with chitinous teeth (g) which converge together in the centre above 

 the opening of the ejaculatory duct ; on the ventral half is a broad 

 chitinous plate somewhat shoe-shaped in lateral view (a and 6), 

 bearing a pair of small toothed processes (h). 



We would like to call attention to the great importance 

 of recognising the mobility of the internal sac and con- 

 comitantly the variation in the position of the sac armature, 

 especially when it closes the median orifice. Unless this 

 is understood the shape of the aedeagus will appear to vary 

 greatly in certain species. In the figures we give, fig. 56 

 shows a side view with sac invaginated, 56h shows the sac 

 partly evaginated, and 56c with it entirely evaginated, or 

 nearly so ; 56a gives a ventral view of 56h. 



