174 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the mouth arms are borne, is attached to the lower floor of the umbrella by 
means of 4 pillars. There is a central mouth opening upon the lower floor of 
the brachial disk. Eight mouth arms arise from the brachial disk. Near their 
distal ends they bifurcate, and a single long filament arises from the place of 
bifurcation of each arm. Thus there are in all 8 of these filaments. These are 
each about 20 mm. in length, and their surface is covered with wart-like pro- 
tuberances. Numerous suctorial mouths are found upon the inner and lower 
sides of the mouth arms. They are surrounded by a great number of small 
tentacles, forming a row around each mouth opening. In addition to these 
small tentacles there are numerous club-shaped papille between the suctorial 
mouths. The surface of these papille is covered with clusters of nematocysts. 
The 4 gonads are V-shaped, the apex of the V being pointed inwards toward 
the centre of the disk. The canal system has been described under “ Generic 
Characters.” The color of the gelatinous substance of the umbrella is dull blue. 
The sub-umbrella, brachial disk, and mouth arms are dull green, and the 8 long 
filaments are deep blue. The 8 radial canals that run to the 8 marginal sense 
organs are green in color. The remaining radial canals, however, are almost 
colorless. There are a number of white spots upon the peripheral portions of 
the exumbrella, and the wart-like protuberances upon the 8 filaments are also 
white. 
The medusa was common in Suva Harbor in December. It swims with 
great rapidity by means of an incessant contraction and expansion of the um- 
brella. This movement is accomplished by the action of a powerful system of 
circular muscles in the sub-umbrella. 
Young Medusa (Figs. 42-44). A young ephyra of this species was captured 
in Suva Harbor on January 11, 1898. The bell was 5 mm. in diameter and 
qnite flat and disk-shaped. There were 8 marginal sense organs. The central 
mass of dark brown pigment granules of the sense organ was developed, but 
the peripheral shell of transparent granules had not yet made its appearance 
(compare Figs. 41 and 44). There were 24 marginal lappets, the 16 ocular 
lappets being about twice as long as the 8 intermediate lappets. There were 
16 radial pouches from the stomach. Eight of these went to the sense organs, 
and 8 to the intermediate lappets. The sub-genital porticus was already pres- 
ent, and the brachial disk was suspended from the floor of the sub-umbrella 
by means of 4 gelatinous pillars exactly as in the adult: The ephyra pos- 
sessed only a simple central mouth opening, having 4 cruciform lips. The 
margins of the lips were lined with a row of short, slender tentacles, with 
knob-like ends exactly like those that surround the suctorial mouths on the 
mouth arms of the adult Medusa. No trace of the genital organs could be — 
detected, but the gastric cirri were represented by 12 short filaments (3 in each 
quadrant). The color of the ephyra was very similar to that of the adult. 
Were it not for the sub-genital porticus and brachial disk, this little Rhizos- — 
toma would resemble, in all respects, the young of the Semostome. We have 
observed the ephyra of an allied genus, Stomolophus meleagris, L. Agassiz, 
that was in a slightly more advanced stage than the one here figured; and in 
