io8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



its fulcrum of movement being the articulation with the lower angle 

 of the first valvifer (B, b). The wide membranous proximal part of 

 the second valvula is broadly united with the ventral margin of the 

 anterior part of the second valvifer (E), but its ramus {rsvl) is at- 

 tached to the anterior angle of the valvifer. Posteriorly the second 

 valvifer bears the short, broad third valvula (A. B, E, 3VI). 



Fig. 35. — Abdomen and ovipositor of Ptcronidca rihcsii (Tenthredinidae). 



A, end of abdomen with ovipositor in natural position. 



B, ninth segment, with proctiger and ovipositor. 



C, left first valvifer and first valvula. 



D, distal part of second valvula. 



E, left second valvifer and second and third valvulae, with united ends of 

 second zmlvnlac turned outward showing long ramus (rJvl) united with second 

 valvifer. 



a, articulation of first valvifer with ninth tergum ; b, articulation of first 

 valvifer with second valvifer; c, attachment of ramus of first valvula to first 

 valvifer ; e, attachment of muscle from eighth tergum on first valvifer. 



The basal mechanism of the tenthredinid ovipositor brings about 

 an opposite movement of the dorsal and ventral valvulae by the inter- 

 action of the two valvifers on each other, and of the first valvifer on 

 the ninth tergum. A dorsal rotation of the anterior end of the second 

 valvifer on the lower point of the first valvifer causes a rotation of 

 the first valvifer on the ninth tergum, and vice versa, with the result 

 that the first and second valvulae are simultaneously moved in opposite 

 directions. 



