58 
PACIFIC SCIENCE, Vol. VIII, January, 1954 
Berkeley and Berkeley (1952) from the Pacific 
area around Puget Sound, with a total of 19 
species involved. It seems likely that further 
observation will reveal the presence of this 
hydroid upon still more sabellids than the 
three from which it has been reported to date. 
The observed difference in size of indivi- 
duals and in colony morphology reported in 
the description of this hydroid does not seem 
to be correlated with the host upon which the 
colony is growing. Colonies with both parallel 
and irregular hydrorhizal nets were found 
upon both of the sabellids reported above 
as hosts for Prohoscidactyla flavicirrata in the 
Puget Sound area. 
Prohoscidactyla circumsahella sp. nov. 
The hydroid and young medusa of this 
species were first described by Hand and 
Hendrickson (1950) under the name of Pro- 
hoscidactyla sp. Since that description appeared, 
a series of medusae of this species ranging 
from small immiature specimens to adults have 
been obtained from plankton from Monterey 
Bay. I am indebted to Mr. Prank Gwilliam 
and Mr. Meridith Jones of the University of 
California at Berkeley for some of these 
specimens. 
As the hydroid and young medusa have 
already been described, it does not seem nec- 
essary to repeat the whole diagnosis at this 
time, but certain salient features are worth 
repeating for the sake of comparison with 
the other two species considered here. 
THE MEDUSA: Adult medusae were collected 
during the months of June and July, 1951, 
and a single specimen during July, 1952. 
A total of nine adult medusae have been 
examined. 
The largest specimen observed measured 
3.0 millimeters, bell diameter, by 2.5 milli- 
meters high. This specimen possessed 32 ten- 
tacles and 28 cnidothylacies. The gonads were 
well developed and occurred in the interradial 
position as four paired masses of simple swol- 
len lobes on the adradial sides of the stomach. 
Eigure Ga-c illustrates the appearance of a 
living, 24-tentacled, adult medusa as well as 
the details of the shape and location of the 
gonads and the lips of the manubrium. The 
manner in which the lips fold seems to be 
characteristic of this species. 
Prom a study of the nine medusae in hand, 
it appears that a rather regular system of 
branching of the radial canals obtains in this 
species, with the result that the adult medusae 
are quite uniform. Of the specimens examined 
only a single one deviated from the pattern 
of development presented in Eigure \d-f. This 
single specimen possessed 25 tentacles, the 
single unusually located tentacle occurring to 
the right of the second order tentacle of one 
quadrant and connected to the second order 
canal by a short canal of its own. In immature 
or developing medusae there is an obvious 
difference in tentacle length, tentacle bulb 
diameter, and radial canal size; the older ten- 
tacles, tentacle bulbs, and radial canals are 
longer or larger, and thus the developing 
complexity of the canal system is readily 
visible. Prom the time the medusae reach the 
l6-tentacle stage until they attain the 32- 
tentacle condition the exact order of appear- 
ance is not precise; therefore, specimens may 
have odd numbers of tentacles, although the 
end result is uniform as judged by the four 
specimens which possessed 32 tentacles. 
Fig. 6. Prohoscidactyla circumsahella. a., Whole me- 
dusa, with tentacles shown on one half only; h, side 
view of stomach; c, aboral view of stomach. 
