HENRY J, FRANKLIN. 213 



sidered here in detail. They are in general much like those 

 of the honey bee, but the tongue and maxillae are much 

 longer than in Apis, the former, when fully extended, reach- 

 ing back to, or often even considerably beyond, the middle 

 of the abdomen. The labial palpi are four segmented and 

 the maxillary palpi normally two segmented. 



Labrum (figs. 51, 103, 107 and 114). — This organ is of 

 some assistance in classification. In Bombus, it is transversely 

 oblong in general form in all castes. The males of Psithyrus 

 are like Bombus in this regard, but in the females of that 

 genus the labrum is rather strongly triangular in general 

 outline (fig. 103). The side margins are always outcurved. 

 The line of attachment with the clypeus is always nearly 

 straight in the middle and in Bombus usually bends forward 

 (away from the clypeus) somewhat on each side. The apical 

 margin is most often nearly straight, but it may bend either 

 outward {Psithyrus females and, to a less degree, some other 

 forms) or inward (fig. 114). If the labrum of the females 

 of some species (e. g. — consimilis, perpexus) is detached, 

 mounted and examined with a microscope or even with a 

 good hand lens, looking toward a strong light, a conspicuous 

 light " translucent area " will be seen near each end. Psi- 

 thyrtis and the males of Bombus do not have these areas. In 

 many species of Bombtis they are also partially or entirely 

 obliterated in the females (queens and workers). In the 

 females (queens and workers) of Bombus, the labrum bears 

 a noticeable median transverse shelf-like projection or carina 

 (fig. 114) near its apical margin. Each end of this carina 

 ends in a somewhat elevated area. These areas are called 

 " tubercular areas " and " tubercle-like areas " in the various 

 specific descriptions in this paper. These areas vary in their 

 amount of elevation in different species, and they usually 

 consist of an irregularly circular, moderately elevated, and 

 rounded ridge enclosing a more depressed area. Between 

 these "tubercular areas" and above the carina, the surface 

 is usually more or less strongly depressed. In Psithyrus 

 females this surface structure of the labrum is often consider- 

 ably modified. The transverse carina is sometimes reduced 



TRANS. AM. ENT. SOC. , XXXVIII. 



