6oo The American Nahiralist. [July. 
partially retracted. Along the sides of the body clusters of 
unicellular algae are seen, which sometimes occur in such num- 
bers as to almost completely conceal the body of the hydroid. 
There is another curious Hydromedusa, which was taken in 
the skimming nets used in pelagic fishing in the Santa Barbara 
Channel. The genus \Yillia is remarkable for the bifurcation of 
the radial chymiferous tubes, as shown in the cut. 
This interesting genus, never before recorded from the waters 
of California, is related to the young of a genus Proboscidactyla, 
and the Medusa figured may belong to this genus. 
One of the most interesting Medusse from the Santa Barbara 
Channel is a little-known genus, Athorybia. Athorybia is a mem- 
ber of the group of Siphonophora known as the Physophorse, 
although it bears little superficial likeness to Agalma and Phy- 
salia, two of the best-known members of the group. 
The anatomy of Athorybia is simple. The most prominent 
structure is an oval float of pink color, from which there hangs 
a tube-like or trumpet-shaped body, as represented in my figure. 
At the base of the float there arises a circle of leaf-like bodies, 
transparent, gelatinous, penetrated from end to end by a tube, and 
crossed in their exterior by motor lines of lasso-cells. Very 
flexible bright pink bodies called tasters hang out from beneath 
the flat leaves, or, as they are called, the covering-scales, and long, 
highly flexible tentacles extend far beyond the tips of these and 
other organs of the body. Each tentacle bears a tentacular 
knot, as it is called, which are lateral branches, enlarged at one 
end, and with the termination divided into three divisions. The 
main body of the knob at the end of the lateral branches is com- 
posed of a spirally-coiled structure, covered by batteries of sting- 
ing cells, and partially enclosed in a covering-sac or involucrum, 
which is extended on one side into a conical projection or apex, 
as represented on the figure. There is but one kind of these 
structures along the tentacles of Athorybia, but in the neighbor- 
ing genus Diplorybia from Florida there are two kinds of these 
The interpretation of the function of the organs of Athorybia 
described above, is in certain respects not difficult. The large 
