152 EXPEDITION OF THE "ALBATROSS," 1899-1900. 



The mouth is a simple round opening at the centre of the sub-umbrella. 

 The fourteen gonads are situated at the centripetal edges of the fourteen 

 stomach pockets. The gonads and tentacles are slightly milky in color, 

 while all other parts of the medusa are transparent. A single specimen was 

 obtained off Kwajalong Atoll, Marshall Islands. It came up in an open net 

 which had been towed between 150 fathoms and the surface. 



(150f — S)f ; Station 220; January 1G, 1900; N. Lat. 8° 38', W. Long. 167° 37'. 



Rhopalonema typicum Maas. 



Homceonema typicum Maas, 1897; Mem. Mus. Comp. Zobl, Vol. XXII., p. 22, Taf. III., 

 Figs. 1-3. 



Plate 5, figs. 21-22. 



Maas describes this species from the west coast of Mexico. We first met 

 with it on September 7, 1899, at N. lat. 6° 41', W. long. 137°. We also 

 found it at the Marquesas and Paumotus Islands, and at Tahiti. It was 

 especially common in surface hauls made at night, and appeared to be most 

 abundant about 3° north of the equator in W. long. 137°. 



The bell is broad and hemispherical, and there is a small solid apical 

 projection. The largest specimen obtained by us was about 15 mm. 

 in diameter, but Maas records one of 20 mm. in breadth. The bell-walls 

 are very thin but are remarkably stiff and rigid, swimming being accom- 

 plished by means of the strokes of the powerful velum which is exceed- 

 ingly flexible. There are eight well developed tentacle bulbs situated at 

 the bases of the eight radial canals. In addition to these there are about 

 twenty-five or thirty smaller tentacles which are interradial in position. It 

 seems probable that the shafts of all of the tentacles were broken off in all 

 the specimens found by us, leaving only the basal bulbs. There are about 

 sixteen exceedingly small otocysts upon the bell-margin, each one of which 

 contains a single spherical otolith. The velum is large, and the contractions 

 of its powerful muscles cause it to vibrate with remarkable rapidity. A 

 well developed system of circular muscles is found in the ectoderm of the 

 sub-umbrella. The proboscis is urn-shaped, the proximal part being nar- 

 rower than the mid-region. There are four recurved lips. There are six 

 gonads, one upon the middle region of each of the radial canals. Young 



