CALKINS: SOME HYDROIDS FROM PUGET SOUND. 345 
uliform, with serrate or entire margin, destitute of operculum and 
with the cavity distinctly differentiated by a perforated diaphragm 
from that of the peduncle; peduncle springing from the sides of a 
simple or a ramified, free or adherent hydrocaulus. Hydranths with 
a trumpet-shaped hypostome. Gonosome. Gonophores adeloco- 
donic, i. e. never issuing from beneath the cover of the gonangium.” 
Obelia. “Trophosome. Hydrocaulus simple or branched, fascicled 
or monosiphonic. Hydrotheca campanuliform, destitute of oper¬ 
culum, pedunculate, with the cavity distinctly differentiated from 
that of the peduncle. Gonosome. Gonophores medusiform, vesci- 
culate planoblasts with shallow umbrella, four radial canals on 
which the gonads are developed, short manubrium with four-lobed 
mouth, numerous rather rigid marginal tentacles whose roots are 
plunged into the substance of the umbrella, otocysts carried each 
close to the base of a tentacle, velum rudimental.” 
He makes a similar difference between the genera Laomedia and 
Gonothyraea. The trophosome is similar in both, the gonosome with 
free-swimming medusa in one (Laomedia), with reduced medusae in 
the other. This division of the genera is as satisfactory as any can 
be when based solely on the presence of gonosomes, but when these 
are absent the problem is as complicated as ever. To offset this 
difficulty, Levinsen has proposed the adoption of a new differen¬ 
tial in the “ diaphragm,” which had been earlier recognized by 
Allman as a familv characteristic. Levinsen claims that the dia- 
ph ragm has a certain definite structure in the various species 
of Campanulariidae and that, according to the similarity of struc¬ 
ture in various cases, the species can be grouped into genera. The 
differences in diaphragms he finds correlate fairly well with the 
mode of growth of the trophosome, and with this differential he 
could retain the older division of the familv as made by Lamou- 
roux. 
In the simplest form the hydrotheca encloses a simple space 
which connects directly with the hollow in the peduncle, but in 
Campanulariidae the connection is not direct, the cavity of the 
hvdrotheca opening into a second space,— the “basal chamber” of 
Levinsen, — which connects with the cavity of the peduncle. The 
basal chamber is separated from the hollow of the hydrotheca by a 
chitinous partition — the diaphragm —Levinsen’s chief differential. 
It is of variable thickness and is perforated by a more or less wide 
aperture for the coenenchyme. According to this observer, all 
