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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



a marginal flange and is visible in both the fore- and the 

 mesocoxa. The metacoxa does not show the separation of a basicosta 

 by external lines or internal ridges. The extreme proximal end bears 

 a rather indistinct, internal marginal ridge only. 



The three articular surfaces (Snodgrass) are largely modified in 

 the different legs. The pleural articular surface of the fore-coxa is 

 present as the medial, proximal margin of the basicosta only. This 

 part is slightly more heavily chitinized. In the mesocoxa the pleural 

 articular surface (b) is more strongly developed. It consists of a 



Fo 



Fig. 25. — Gnathotriclius matcriarius Fitch : A, forecoxa, lateral aspect ; B, meso- 

 coxa, C, metacoxa, both ventral aspect. 



Be, basicosta; Bex, basicoxite; F, femur; Fo, fossa; Tr. trochanter; a, basicostal suture; 

 b, pleural articular surface; c, outer ring of fossa; d, inner ring of fossa; e, anterior coxal 

 suture; /, internal ridge; p, basicostal ridge of trochanter; h, condyle of trochanter; i, 

 trochantero-femoral suture. 



projection of the basicosta. In the metacoxa a hooklike structure (b), 

 which is basally fused with the anterior coxal suture, may be con- 

 sidered as the pleural articular surface. 



The articulation of the trochantin is monocondylic with the fossa 

 in the coxa. The fossa (Fo) is a circular, conelike, impression on 

 which two main parts are clearly defined; the outer ring (c) with a 

 ridgelike elevation on the external surface of the coxa and the inner 

 ring (d) or bottom which bears a heavily chitinized knob on the inner 

 surface. It is most probable that the outer ring corresponds to the 

 anterior, the inner ring to the posterior or distal articular surface of 

 Snodgrass. Each coxa has opposite to the fossa a circular opening in 



