168 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 
filaments (arranged in two series, a and b below) together with a con- 
nective tissue sheath (¢ below). 
(a) First series, composed of one yellow filament (variety 1) and two 
white filaments (variety 2), the latter applied one along each side of 
the yellow filament. One of the white cylinders is always flexuous, the 
other always straight and without undulations. 
(b) Second series, consisting, like the first, of a yellow filament (vari- 
ety 1) accompanied by two semitransparent, hyaline, whitish filaments, 
which resemble the previously described filaments in being continuous 
and endless, but which appear not to be composed of cells. They consist 
only of a thin wall filled with a semiliquid, finely granular substance. 
One of these whitish filaments is flexuous and undulating; the other, 
instead of being straight throughout its whole length, undulates a 
little from place to place. 
(c) Sheaths formed of connective tissue of the host, penetrated by 
delicate capillaries. 
Parasitic mass (as a whole).—Showing through the thin covering of 
transparent mucous membrane of branchial cavity as a grayish or 
whitish mass of convoluted strings (varieties 1 and 2), strewn with small 
brown masses (variety 3) of the size of a pea. Size of parasitic mass 
varying from that of a millet seed to that of a large goose egg. Some- 
times voluminous on one side and small on the other; sometimes com- 
posed of two or three separate lobes. Form inconstant, generally con- 
sisting of round or elongatedlobes. Arteries and veins few, extremely 
delicate; derived from vessels of neighboring muscles, which, with the 
loose submucous tissue, form the only bond between the mass and the 
tissues of the host. Injection with mercury (of the connective tissue 
sheath, described above under variety 1) demonstrates that the mass 
consists of closed lobules. When filled with mercury, no escape of the 
metal occurs unless greater pressure produces rupture. When very 
small, the mass may be unrolled and shown to consist of a convoluted 
string. 
Habitat, ete—Submucous connective tissue of branchio-abdominal 
septum (between scapular and last branchial arch) of Sciena umbra. 
Among 9 fish (male and female) examined in September, it was absent 
in 4. The size of the 5 hosts varied from 1:30 m. to 1:70 m. Sometimes, 
but rarely, variety 3 exists alone, the usual condition, however, being 
that varieties 1 and 2 are present together and are accompanied by 
small colonies of variety 3. 
Nature.—Robin regards it as referable to the Diatoms. Lieberkiihn! 
says that: 
The psorosperms of some marine fishes recently described by Robin behave in 
every respect like Trematode eggs. 
Whatever other view be taken of its affinities, this species is cer- 
tainly not myxosporidian. As remarked above (p. 72), the generic 
name must follow the type species. 
1 Miiller’s Archiv., 1854, pp. 10-11. 
