1968] 
Matthews and Matthews — Trypargilum 
291 
The unique cocoon of T. striatum , with its strongly flared anterior 
end, would appear to justify the placement of this species in the 
Punctulatum group by itself. Interestingly, the distinctive shape of 
this cocoon has caused at least three different authors to describe it 
(Krombein, 1956, 1967; Balduf, 1961; Medler, 1967). By contrast, 
the cocoon of the common pipe organ wasp, T . politmiij has to our 
knowledge never previously been described in detail, despite an ex- 
tensive literature on that species. (Also, surprisingly, only one 
extensive prey analysis has been made for T. politum ; see Table 3.) 
Trypargilum politum cocoons (Fig. 2) are the largest in the 
genus, almost twice the size of those of T. arizonense. As in other 
species of the genus, the cocoon is enveloped in a delicate silken 
matrix; however, incorporated into the matrix is a 2-4 mm wide 
girdle of sand grains encircling the posterior end of the cocoon. This 
girdle is easily brushed off when the cocoon is handled. The anterior 
end is rounded as in T. tridentatum tridentatum , but rather than 
being smooth, bears a conspicuous crown of larger, unincorporated, 
unvarnished sand pebbles (see Fig. 2). Also, the crown is distinctly 
lighter in color, appearing tan whereas the remainder of the cocoon 
is dark reddish brown. The surface of the cocoon walls has the 
texture and appearance of varnished coarse sandpaper, due to nu- 
merous sand grains incorporated into it; in this respect as well as in 
the presence of a pebble crown and girdle, the cocoons of T. politum 
differ from those of all other known Trypargilum species. The source 
of the cocoons was a 12-celled T. politurn nest in the Museum of 
Comparative Zoology collection. Nine cocoons containing dead fully 
formed females averaged 19.0 mm (18.0-20.0 mm) and two cocoons 
containing males averaged 17.5 mm (17.0-18.0 mm); one cell had 
fragmented dried spiders. 
Conclusion. In summary, prey preferences, cocoon structure, 
larval and adult morphology are in general agreement in indicating 
at least four phyletic lines within the genus Trypargilum. The 
analysis of biological characters might profitably be extended to 
include other ethological, architectural and morphological characters; 
unfortunately, the fragmentary, often isolated observations in the 
present literature are insufficient for such an analysis at this time. 
However, the ready availability of most Trypargilum species through 
the trap nest technique makes them a particularly suitable subject 
for such an evolutionary study. 
