340 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
sometimes abruptly linear from the body, which then appears to be shouldered ante- 
riorly (Fig. 4) ; at other times the whole anterior part of the body becomes exceediugly 
attenuate ; sometimes it is swollen or truncate at the apex (Fig. 5) ; sometimes rounded 
linear or spatulate ; sometimes triangular, wedge-shape, and even retracted until it 
is no longer distinguishable. The bothria, or suctorial pits, are lateral, and the head 
is flattened so that its broadest aspect is seen when the worm is lying on its edge or 
shorter diameter (Fig. 9). The edges of the bothria are rather thin and lip-like and 
are often crumpled or thrown into sinuous folds owing to longitudinal contraction of 
the head (Figs. 1, 2, 3, 7). 
The color is usually ivory white or translucent white with an occasional tinge of 
yellow. 
There is no indication of genital organs other than that mentioned in my previous 
paper of clusters of nuclei, shown in thin sections, lying along the median line near 
one of the lateral faces, thus indicating that in the adult the genitalia are median and 
the apertures lateral. 
DISTRIBUTION. 
This parasite occurs, so far as known, only in the Eocky Mountain trout {Salmo 
mylciss). I have found it in the trout of Yellowstone Lake, Yellowstone Eiver above 
the lower falls, and in Heart Lake. I did not succeed in getting any fish from below 
the lower fails, for examination. I am told, however, that wormy trout are never found 
in the river below the lower falls. It is very probable, however, if careful search were 
made for them, that an occasional trout in the river and its tributaries below the lower 
falls would be found with cysts of this parasite. At the Grand Canon Hotel I exam- 
ined some trout which were said to have been caught below the upper falls and found 
one with cysts in the abdominal cavity and a large larva among the abdominal muscles. 
In Heart Lake I found the trout not infrequently infested with this parasite, occurring 
in cysts and free on and among the viscera, but not among the muscles. 
Dr. Jordan reports that the trout of Eiddle Lake, which drains through Solution 
Creek into Yellowstone Lake, are apparently free from parasites. It may be that this 
conclusion would have to be abandoned if an examination were made of several of the 
large trout of that lake. 
Following is an abstract of notes made at the time of collecting, inserted here for 
the purpose of showing the actual occurrence of this parasite in the fish examined : 
HEART LAKE. 
All of these trout were taken in front of our camp near the Eustic Geyser Basin, 
with trammel-net and hook and line. 
(1) July 26. — Found one trout near shore with wounds on its sides, from the effects 
of which it was dying ; had evidently been struck by a fish hawk ; no dibothria. 
(2) Ten trout examined ; a few cysts found on serous coat of intestine and pyloric 
cceca; only two of the number had many cysts, about a dozen each. The serous coat 
of the intestine of these two was somewhat congested and the swim-bladder was more 
deeply colored than in the others. 
(3) July 28. — Eight trout examined, most of them with a few cysts, as in Eo. 2. 
In one there was a larval Dibothrium in the abdominal cavity on the outside of the 
