Fossorial Hymcnoptcra of North America. 411 



Family Nyssonid^e, Leach. 



In this group, the head, compared with that of the preceding family, 

 is much more cylindrical in outline; the vertex is higher, more convex, 

 and inclined, especially in Larra, to he compressed antcro-posteriorly. 

 The front is narrow, eyes long and narrow, and the antennae more cla- 

 vate than in the Crahronidse generally. The clypeus is long and nar- 

 row, compared with the Crahronidae, approaching in Stizus somewhat 

 the form (if that of Bcmbex. Labium large, lunate, exserted ; mandi- 

 bles large and stout, iucurved, often subspatulate in form. The thorax 

 is oblong square, as the propodeum is square, aud generally quadran- 

 gular posteriorly, or armed with acute spines; enclosure polished and 

 smooth or striated. The wings are long and narrow; the outer edge 

 of the 2d sub-median cell being straight, while the cell itself is broad 

 triangular, outer cells large aud long — present in the typical genera. 

 The abdomen is sessile in the typical genera, and near the basal 

 ring is short and broad where its form is elongated conical, and 

 clavate in the pedicellated genera. 



The genera all differ from those of the Crabronidae in the shorter, 

 more transverse head, much narrower front, the long narrow clypeus 

 and exserted visible labrum ; in the elongated thorax ; the long slender 

 legs, and long narrow wings, with the large broad sub-triangular 2d 

 sub-median cell. 



This is a difficult group to limit, but we offer the present classifica- 

 tion for the consideration of entomologists, believing it to be an ap- 

 proximation to a true one. It evidently connects with the Bembeci- 

 da3, as we have a Bembex from Cuba, remarkably resembling some 

 European species of Larra; and with the genus Stizus. The tendency 

 of the labrum to become elongated in Larra, culminates in Bembex 

 and AToneduIa. 



This family is easily subdivided into three subordinate groups, which 

 we would for the present consider as subfamilies, and which rank in 

 value with the Crabronidae or Pemphredoninae in the preceding 

 family. 



Of the Trypoxyloninae, the genus Trypoxylovt is the only represen- 

 tative we have in the North American fauna. Though its wings are 

 like those of the Crabrouidao, in its other characters it departs too 

 widely from that group to be retained in it, as many authors have 

 done, and is on many accounts still difficult to locate in the present 

 group. For this reason it is one of the most interesting genera among 

 the Fossorial families, and any light thrown on its developmental his- 



