1921] Metcalf: Genitalia of Male Syrphide 197 
some of which originate on it and others of which attach to it. At 
its apex it supports the chitinous box together with any ejaculatory 
process, ejaculatory hood and internal lobes that may be present. It 
evidently functions in supporting, reinforcing and directing these latter 
parts during copulation; at which time they apparently have movements 
somewhat independent of the penis sheath and its appendages. 
Some idea of its variations will be gained from the following state- 
ment. It is practically straight and cylindrical in Chilosia, Lasiophthicus, 
Eristalis, Volucella, Copestylum, etc., and may be either long and 
slender as in Pipiza and Hammerschmidtia or short as in Baccha (Note 
Figures 17, 19, Plate XI; 56; Plate XIII; 67,:Plate XV) or long very 
heavy and enlarged basad, as in Mesogramma. Very commonly it is a 
bent rod, conforming often to the general shape of the penis sheath as in 
Allograpta, Blera, Condidea, Brachyopa, Tropidia, Syritta, etc., (Figs. 
93, Plate XVI, 114,. Plate XVIII), or bent at base only as in Pipiza 
‘spp., (Fig. 35, Plate. XII) or bent to the left at base as in Chilosia (Figs. 
28, 29, 30, Plate XII). Frequently instead of being cylindrical, it is 
compressed asin Milesia, Callicera, Temnostoma, Bachyopa, Asemosyr phus 
and Mallota posticata; sometimes distinctly sword-shaped as in Melano- 
stoma and Cnemodon spp. It tapers more or less evenly from apex 
towards the base in Helophilus spp. (Fig. 83, Plate XVI). It is com- 
monly expanded at its base as in species of Chrysogaster, Criorhina, 
Triodonta, Mesogramma, Tropidia, Syritta, and Asemosyrphus (Figs. 
37,47, Plate X; 70, Plate XIV), rarely about the middle, as in Sericomyia 
and S‘phegina sp. (Fig. 76, Plate XIV) and almost always more or less 
so at its apex in adaptation to the chitinous box. This latter expansion 
may be noted, for example, in Paragus, Platychirus, Allograpta, 
Brachyopa, Somula, Milesia, etc. (Figs. 5, Plate X; 25; Plate XI, 67, 
Plate XV; 114, Plate XVIII). Sometimes the expansion has associated 
spurs or thorns, as in Pipiza spp., or it may be flattened and tongue-like, 
projecting cephalad as in Syrphus, Eristalis and Chrysotoxum, or such 
tongue may project caudad from the apex as in Sphaerophoria and 
Sphegina spp.; or it may be a flattened transverse plate. In a number 
of cases there are sharp thin keels or ridges running lengthwise of the 
apodeme probably of use for the attachment of muscles. Such keels 
may extend full length or over only a part of base, apex or middle. 
Such a keel is found on the caudal side of the apodeme in Didea fasciata 
fusctpes, and in Pipiza spp. (Fig. 25, Plate XI), while a similar ridge 
occurs on the cephalic face in Eupeodes volucris and Syrphus spp. 
I have not found it in the paired condition in this family, although 
it is forked near the apex in Rhingia (Fig. 32, Plate XII) and from about 
the middle, distad, in Paragus tibialis (Fig. 11, Plate X); while in Teuch- 
ocnemis it is forked at the base. In Pterallastes thoracicus (Fig. 97, 
Plate XIX) it is triradiate toward the base, the median ray shorter, and 
standing more cephalad, the lateral rays extending caudad. In Sphegina 
petiolata (Fig. 75, Plate XIV) it is also split into three forks toward 
the base, but all three of these forks stand in the median sagittal plane. 
Rarely the sustentacular apodeme appears to be wanting as in Microdon. 
