CRABRONID^E. 161 



slight cocoon, not at all comparable with that of Crabro ; the 

 walls of the cell being simply lined with silken threads. Under 

 other circumstances, i. e. where the cells are more exposed, it 

 is not unlikely that a more elaborate cocoon may be spun. 



Mr. James Angus has bred numerous specimens of Rlwpa- 

 lum pedicellatum Pack., from stems of the Rose, Corcorus, Ja- 

 ponica, and Spiraea, grown in hot-houses at West Farms, N. Y. 

 The larva is a quarter of an inch long. 



The following genera belong to the subfamily Pemphre- 

 donince : 



The genus Stigmus, as its name indicates, may at once be 

 known by the very large pterostigma, as well as the unusually 

 small size of the species. The body of the larva is moderately 

 long and slender, cylindrical, tapering slowly towards both ex- 

 tremities. The rings are short, very convex, subacutely so, 

 and the larva is of a beautiful roseate color. Stigmus frater- 

 nus Say burrows in the stems of the Syringa, of which speci- 

 mens have been received from Mr. Angus with the larvae and 

 pupae. 



In Cemonus the front narrows rapidly towards the insertion 

 of the mandibles, and there is a short triangular enclosure on 

 the propodeum, while the abdomen is shorter and thicker than 

 in Pemphredon, a closely allied genus ; the pedicel is also 

 longer. The larvae of Cemonus inornatus Harris live in irregu- 

 lar burrows in the elder, like those of Rhopalum from which 

 they have been reared by Mr. Angus. They are known by the 

 broad flattened head and body, serrate side and tergum of the 

 body, and large, conspicuously bidentate mandibles, as well as 

 by the peculiarly flattened abdominal tip. 



In Passalcecus the labrum is very prominent, while the man- 

 dibles are very large, widening towards the tip, and in the com- 

 mon P. mandibularis Cresson they are white, and thus very 

 conspicuous. This species burrows in company with the other 

 wood-wasps mentioned above in the stems of the elder and 

 syringa. The cells are lined with silk. The wasps appear 

 early in June. Their nests are tenanted by Chalcids. The 

 female stores her cells with Aphides, as we have found them 

 abundantly in stems of plants received from Mr. Angus. 



The genus Psen seems to be a degraded Cerceris, but the 

 11 



