WILLIAMS: LARRID^ OF KANSAS. 181 



The Larrld^ of the genus Tachytes include our largest and 

 most bee-like species. Tachysphex, though by far the best 

 represented of the genera, is made up of rather inconspicuous 

 wasps which can be secured in variety only by dint of close 

 collecting. Genera such as Niteliopsis, Plenoculus and Mis- 

 cophus are composed of small forms; it is by reason of this 

 diminutive size, their activity, as well as special habitat, that 

 many more species will eventually be discovered. 



The Larridfe of the United States range from 3 mm. to 

 about 2.3 mm. in length. 



The ocelli or simple eyes present characters of first im- 

 portance within the family; the mandibles perhaps stand next 

 in order ; which is the case because these two organs are sim- 

 ilar or nearly so in both sexes. Venation, while of great 

 importance within the family, is often variable, particularly 

 in the smaller forms. Considered on a broad basis, the above 

 characters may be said to be of supergeneric value.* The 

 more relative form and position of the ocelli, the variation in 

 the mandibles, legs, venation, pygidium, eighth ventral seg- 

 ment ( J ) , the convergence or divergence of the compound 

 eyes, are commonly of generic importance. The often pro- 

 nounced sexual differences, found, for example, in the an- 

 tennae, pygidium, armature of legs, and the clypeal outline, 

 are of generic and specific value. It is owing to these marked 

 structural as well as color differences, and to the frequent 

 absence (apparent or real) of good characters common to both 

 sexes, that renders impracticable, in those genera containing 

 a goodly number of species, the construction of one specific 

 key to include both sexes. Very important specific characters 

 are : The character of the anterior margin of the clypeus ; the 

 width of the interocular space at the vertex ; the distinctness, 

 shape, armature and punctures of the pygidium ; the compara- 

 tive length of the antennae and their joints, as well as the form 

 of any of the latter; the sculpture of the head, thorax and 

 propodeum (closeness and size of the punctures, striations, 

 granulation, etc.) , and the color. The latter, while remarkably 

 constant in some groups, is quite variable in others, and should 

 therefore be used with care. 



* There may prove to be characters even more far-reachins than those just mentioned 

 (and as suggested by eerlain writers) to be found in the sternal region of the thorax The 

 nnnith parts, which for their proper study would require careful and tedious dissections 

 could possibly furnish clews as regards the status of the Larridn?. 



5-Univ. Sci. Bull.. Vol. VHI. No. 4. 



