Patton] 378 [January 21, 
mental material, as those of later times. With very rare exceptions, — 
these primitive conglomerates cannot now be found. And the ques- 
tion is, if they have not been converted into crystalline schists, 
what has become of them? At the same time, the present condition 
of such remnants as are left points very strongly to this solution of the 
problem, and indicates that the first step in the destruction of the con- 
glomerate, as such, has been the distortion of the pebbles. 
By these considerations, I am led to the conclusion that the distor- 
tion of pebbles, instead of being an exceptional, is probably a very 
general, phenomenon ; and it seems to me likely that, since the forma- 
tion of conglomerates first began, more pebbles have suffered distor- 
tion than have escaped that process. 
. 
SoME CHARACTERS USEFUL IN THE STUDY OF THE SPHECIDAE. 
By W. H. Patron. 
PELOPOEUS Latr. (1804). 
American type: P. caementarius (Drury) Smith. 
Black, with markings usually of a yellow color. Clypeus bilobed 
at the apex, rarely entire (more narrowly produced, and the lobes 
not so distinct in the male). Mandibles of the female broad, armed 
with a distinct tooth near the apex. Sutures of the meta-episterna 
distinct. Claws of all the tarsi armed with a short tooth near the 
middle; two bristles on base of pulvillus, and four above them. 
Petiole of the abdomen as long as the entire thorax. Cocoons with- 
out any layer of white silk, the black plug at the end uncovered. 
CuatyBion Dahlb. (1843). 
Type: Chalybion caeruleum. (Sphex caerulea Linn. Syst. Nat., 1, 
941; Chalybion cyaneum Dahlb.) 
Blue or violet. Clypeus tridentate at the apex, and in the female 
sometimes with a small additional tooth at each side. Mandibles of 
the female slender, of even width throughout, and unarmed (Ch. 
caeruleum); or, short, broad and blunt, and armed with a blunt tooth 
near the apex (Ch. Zimmermanni). Sutures of the meta-episterna 
indistinct beneath the fovea. Claws of the posterior tarsi un- 
armed; two bristles on the base of the pulvillus, and six above them. 
Petiole of the abdomen not so long as the metathorax. Cocoons 
with a loose exterior layer of white silk, which covers also the black 
plug at the posterior end of the cocoon. In this genus, as well as in 
