160 HYMENOPTERA. 



Crabro singularis Smith, was discovered by Mr. C. A. Shurtleff 

 boring in a post. 



In Thyreopus, the body is slender, and the forelegs are 

 curiously dilated in the males, often forming a broad expansion, 

 and so dotted as to present a sieve-like appearance, while the 

 head is much shorter, being more transverse. T. latipes Smith 

 is known by the broad, long, acute, mucronate, shield-like ex- 

 pansion of the fore tibia, which is striped with black, at the 

 base. 



The species of Rhopalum are usually blackish, without the 

 gay colors prevalent in the genera before mentioned ; the legs 

 are simple, and the abdomen is long and slender, with a long 

 peduncle. The body of the larva is short and thick, tapering 

 rapidly towards each extremity ; the segments are convex, 

 those of the thorax especially being smooth, broad, and regu- 

 larly convex, while the abdominal rings are provided with 

 prominent tubercles. The tip of the body is quite extensible, 

 and when protruded is subacute, terminating in a small knob- 

 like body, formed by the last ring. The larvae of this genus 

 differ from those of the Vesparim audApiarice known to us 

 by having a few hairs scattered over the body. 



In the pupa the antennae, in their natural position, do not 

 quite reach to the second pair of trochanters, and reach only 

 to the tip of the maxillary palpi. The tip of the abdomen is 

 very acute and elongated unusually far beyond the ovipositor. 

 On the head, between the ocelli and antennae, are two very 

 prominent, acute tubercles, and the abdominal segments are 

 dentate on the hind edge. Thus both the larva and pupa 

 would seem, by their anatomy, to be unusually active in their 

 loose, illy-constructed cells, which do not confine their food so 

 closely as in the other wasps, as the insects on which they prob- 

 ably feed have a greater range in their rather roomy cells. April 

 18th we opened several stems grown in the open air, and 

 found both larvae and pupae ; the latter in different stages of 

 development. The cells were placed in the closely packed 

 dust made by the larva of an JEgeria, or directly bored in the 

 pith of the plants. There were six such cells, each with its 

 inhabitant, within a space an inch in length, some laying cross- 

 wise, others along the middle. The larvae spin but a very 



