Fig. 22 represents four rows of prestomal teeth and the corresponding portion of the 

 labellum seen from the oral surface. In the upper part of the figure three of the 

 central pseudo-tracheae, showing the alternate bifid and flattened ends of their 

 rings and the longitudinal fissures, are represented. Each passes into a collecting 

 tube with non-bifid rings which terminates by a spout-like opening between the 

 distal extremities of two rows of prestomal teeth. The inner, shortest set of 

 teeth are lightly shaded. They are unbranched and articulate with the lateral 

 plate of the discal sclerite by their strong proximal extremities. The teeth of the 

 intermediate set, which are more darkly shaded, branch behind the distal 

 extremities of the inner set. The branches diverge to each side of the corre- 

 sponding inner teeth to articulate with the lateral wall of the discal sclerite. The 

 teeth of the outer set are most darkly shaded. The two central teeth of this set 



