I I I 
much larger and stiffer than 1', or P., recurved and horn-like, the 
component segments with jjroduced and spinous distal ends .... Cenometra 
b- lo arms; size small; at least the outer cirrus segments nearly or quite 
as long as broad, bearing dorsally a serrate transverse ridge (sometimes 
two, a proximal and a distal) or long spines 
c^ P, shorter, smaller and weaker than P, ; P,, and usually also P.,, 
elongated, enlarged and stiffened, with the distal edges of the 
segments produced into spinous overlapping borders, or with the 
distal portion of the prismatic angles produced into rounded or 
pointed processes 
d' 30 or more cirrus segments of which only the basal bear transverse 
ridges these after the proximal fourth of the cirrus transforming 
into very long dorsal spines; P., has at most 12 segments . . Cotylometra 
d- 25 or fewer (usually about 20) cirrus segments, of which all but 
the terminal bear transverse ridges; P^ has at least 15, and 
usually about 20, segments Oligometra 
c'- Pj the longest and stoutest pinnule on the arm 
d' the third-fifth segments of the genital pinnules more or less 
expanded laterally to protect the genital glands; a single median 
transverse ridge on the cirrus segments 
e' P,, though longer and stouter than P.,, not exceptionally so; 
median transverse ridge on the cirrus segments of moderate height Austrometra ') 
e- Pj much stouter than P„, and so enlarged basally as to cause 
the second brachial to appear like an axillary; median ridge 
on the cirrus segments very high Analcidometra 
d- no expansion of the genital pinnules ; the cirrus segments bear 
two transverse ridges, a proximal and a distal Oligometrides 
Fa absent 
b' more than 10 arms 
c^ P^ as long as, and similar to, P^; IIBr series commonly 4 (3 -|- 4); 
outer cirrus segments with a low dorsal transverse ridge .... Petasometra 
c" Pj shorter than P.,; all the division series always 2; outer cirrus 
segments somewhat shorter than the proximal, bearing paired or 
tripled dorsal spines which on the terminal become resolved into a 
single median spine, or a median carination 
d' Pj much smaller, weaker and more slender than the enlarged 
and stiffened P„; 10—30 arms; 21 — 30 cirrus segments; outer 
cirrus segments with paired or -tripled dorsal spines, which become 
a single median spine terminally Cyllometra 
l) Genotype Oligcmctra ihelidis H. L. Clark, 1 909; this genus is only known from souihe.istern Australia. 
