74* ON TWO SPECIES OF SPHEX. 



I have however seen some individuals which had yellow spots 

 on the thorax, in front of the wings. 



The other sphex, No. II. Plate I. (probably the Pennsylva- 

 nica of Linnasus) differs from the former in many particulars 

 of form and colour. Linmeus's description runs thus : 



Nigra, abdomine petiolato atro, alis subviolaceis. Habitat 

 in Pennsylvania. 



The specific differences are as follows : 



The head is broad, the nose blunt and emarginate, his tho- 

 rax is longer in proportion, the petiole of the abdomen very 

 long, the hook is wanting, the abdomen conical and elegantly 

 formed. The general colour is a dark blue approaching to 

 black, but on the thorax are many yellow spots, and the legs, 

 thighs, and feet are also spotted with yellow. His antennae 

 are longer than in No. I. and he carries them less upright, and 

 often curls them. No. II. Fig. 2. is an enlarged view of his head. 



The figures both of the coerulea and Pennsylvanica are ex- 

 actly the size of the live insects, and an attempt is made to imi- 

 tate accurately their manner when alighting on their cells. 



The cells both of the S. coerulea and Pennsylvanica are 

 built of clay collected in moist places; but their appearance, 

 and mode of contruction is very different. 



The S. coerulea chuses, in the open air, the south side of 

 a rock, or of the trunk of a tree for his structure. He then 

 seeks by the side of a stream for his materials. He scrapes 

 the clay together with his feet, and working it into as large 

 a round ball as he can well carry off, he begins by plaistering 

 the stone or wood with a thin coat. He spreads the clay with 

 his head, uttering a shrill sound during his work. He then 

 flies oft" for another lump, and by degrees forms the upper 

 ridge of his cell. He afterwards adapts a second ridge to the 

 first, working alternately on each side, frequently going into 

 the tube thus formed, and making it perfectly smooth in the 

 inside. In this manner he compleats a tube of 3 or 4 inches 

 long, before any attempt is made to carry in provisions for 

 the young brood. 



