67 
e. Lateral spines of 9 about twice as long as those of 8; 
length of ventral surface of 9 at middle about one 
half its basal width; abdomen more than thrice as 
long as broad. 6. vastus. 
d. Lateral spines of 9 slender, elongate-acuminate, incurved 
apically, nearly or quite as long as the distance to the 
median tooth of the segment; labial apical hook not 
projecting beyond the teeth. 9. externus. 
AA. Three pairs of lateral spines, the first pair very small; 
teeth of lateral labial lobes mostly distinctly separated 
by rather deep incisions, and obliquely truncate; medi- 
an lobe rather prominent, a small projecting tooth at 
middle ; side margins of 9 entire, more or less fringed 
with soft hairs, 10 (except in sp/catus) as long as, or 
longer than, wide; only a trace of a median posterior 
tooth on 9. (Arigomphus Needh.) 
ff. Last three segments evenly tapering, length of ventral 
surface of 9 at middle about three fourths of its basal 
width, 10 wider than long; traces of dorsal hooks; 
labial apical hook prominent, toothed on its inner 
side but not appearing bifid. 10. spicatus. 
f. Last three segments concavely tapering, length of ventral 
surface of 9 at middle about equaling its basal width, 
10 longer than wide; a low scurfy median abdominal 
ridge. 
gg. Labial apical hook as in spicatus; lateral spines of 9 
not over one fifth as long as the inferior append- 
ages. Ll. australis. 
g. labial apical hook and outermost tooth united to form 
a prominent bifid apical tooth. 
hh. Lateral spines of 9 not over one fourth as long 
as posterior appendages. 12. willosipes. 
h. Lateral spines of 9 about as long as inferior append- 
ages. 13. pallidus. 
A, Four pairs of lateral spines (minute in spiniceps); labial api- 
cal hook large and strongly incurved; teeth few, 0-5, 
