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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



The considerable variation in the form and relative size of the 

 labrum is very hard to classify because of the large number of slight 

 variations which grade from one to the other. Figure 14 shows a few 

 of the types. The presence of the membranous processes, such as on 



Intrafamily variation in the labrum. 



A, Stenus sculptilis Csy. B, Xenodusa sharpi Wasm. C, M icr ope plus punctatus 

 Lee. D, Liparocephahis brevipcnnis Makl. E, Pscudopsis obliterata Lee. F, Tany- 

 rhinus singularis Mann. G, Lithocharis ochracea (Grav.). H, Stilicus angularis 

 Er. I, Astenus discopunctatus (Say). ], Pinophiliis parvipennis Csy. K, Trachy- 

 sectus confluentus (Say). L, Lathrotropis jacobina (Lee.). M, Osorius mundus 

 Shp. N, Tachinus limbatits Mels. O, Platystethns americanus Er. 



Osorius (fig. 14 M) and Platystethns (fig. 14 O), is definite and 

 usable, as well as the entirely glabrous character of Stenus (fig. 14 A). 

 The variation in the form and structure of the mandibles is ex- 

 tremely great. Every gradation is found between massive blunt types 

 with a large molar area, such as Micropeplus (fig. 15 C), and the very 

 slender acute type without mola, such as Astenus (fig. 15 L). In some 

 the terminal tooth is the only one present, as in some species of Geo- 



