176 
The dorsal portion of the basal segments of Pd is visible between the lIBr series. 
The dorsal profile of the arms is smooth. 
A similar specimen has 28 arms; eight of the lIBr series are 4(3 + 4) and two are 2; 
the cirri are from 25 mm. to 34 mm. long with 20 — 23 segments. 
The remaining three examples are small, with 20, 19 and 17 arms. 
3. Crossometra septentriotialis (A. H. Clark). 
A. H. Clark. Proc. U.S. National Museum, vol. 34, 1908, p. 312 [Cliaritometra distincta). 
Proc. U.S. National Museum, vol. 39, 191 1, 554 {Fachylometra septentrionalis). 
Perissometra A. H. Clark. 
Key to the Species of the Genus Perissometra. 
aj Proximal portion of the animal abruptly constricted, the sides of the I Br 
series, as seen in lateral view, being nearly parallel, but the sides of the IlBr 
series and arm bases divergent; 14 — 20 arms 75 mm. long; lIBr 4 (3 4- 4); 
cirri XX — XXV, 18 — 23, all, or most, of the segments longer than broad 
(Meangis Islands; 900 Metres) angusticalyx 
a^ No constriction of the proximal portion of the animal 
b^ 14 — 20 (usually 20) arms 
c^ ilBr 2; rather slender; cirri with all of the component segments longer 
than broad 
d^ o.ssicles of the division series and brachials each with a broad low 
inconspicuous median keel which persists to the end of the arms ; 
distal edges of the discoidal brachials beyond the second prominently 
and abruptly everted, of the more distal triangular brachials produced 
and overlapping; arms J4 — 20, 170 mm. to 175 mm. long; cirri 
rather short and weak, XX — XXX, 17 — 22, 30 mm. to 37 mm. 
long (S a h u 1 Bank and the K e i Islands to the Philip- 
pines; 104 — 140 Metres) patula 
d- ossicles of the division series with the dorsal surface unmodified, or 
with a more or less developed broad rounded tubercle ; no eversion 
of the distal borders of the brachials; 12 — 16 arms 250 mm. long; 
cirri very long and stout, XX — L, 18 — 31 (usually 28 — 31) 55 mm. 
to 70 mm. long (Sahul Bank and Timor to the Kei Islands; 
252 — 520 Metres) robusta 
c" IlBr 4(3 + 4); stout; ossicles of the division series and brachials each 
with a low median rounded tubercle which becomes obsolete in the 
outer half of the arms 
d' brachials with smooth and unmodified distal edges and a slightly 
swollen dorsal surfaee; profile of the division series and arm bases 
diverging at an angle of slightly less than 90°; arms 205 mm. long; 
