140 
Psyche 
[J une-August 
the lower border, and are of no significance. The basal part of 
the uncus tends to be a little rounded at the sides, but this varies, 
as does its width. Fig. 5 shows an average specimen; in others 
the spear-head maybe shorter and broader, or it may be narrower. 
The juxta resembles a bisected cone, the flat surface against the 
manica, and varies much in length and breadth; in most speci- 
mens it is evenly tapered to a rounded point, but in two the 
end is broad and blunt. Figs. 6 and 7 illustrate two extremes. 
The sedceagus is similar in shape to vittata and radians > 
consisting of an irregular chitinous tube with a slight double 
curve in the sagittal plane, the duct entering thru its dorsal 
surface just distal to the base. Size and details of shape and 
curvature are subject to individual variation in all the species. 
On the right lower lateral and extending partly onto the ventral 
aspect of the distal portion is the area of heavy chitinization 
which I have called the callum. Distally it is produced into a 
stout, hook-like spine, which points at right angles to the axis of 
the sedoeagus, and the whole hook-like structure is sharply bent 
laterally. The callum tapers proximally, and the proximal part 
becomes twisted nearly at right angles to the distal portion due 
to the upturning of the lower edge, and is often curved toward 
the dorsum. This peculiarity is particularly well marked in the 
specimen selected for Fig. 1. The distal edge of the callum forms 
part of the boundary of the orifice, and the vesica is attached to 
it; elsewhere the callum blends into the normal chitin. Wide 
variations are found in the length and width of the callum, and 
in the size and shape of the spine; in all the specimens examined, 
however, the proximal portion showed the characteristic twist. 
One aberration was found with small callum and a bifurcate 
spine (Fig. 4). Nais showed a much smaller range of variation 
in the genitalia than the next species. 
A. vittata (Figs. 8-16) bears an exceedingly close resemblance 
to nais in the genital structures. The variations in claspers, 
uncus, and juxta in each species grade into each other so that it 
is often impossible to tell from one organ alone to which species 
it belongs. The claspers of vittata vary along the same lines as 
those of nais, but the range of variation is greater. The average 
form of clasp is shown by Fig. 13. Its close similarity to that of 
