554 REPORT OF COMMISSIONER OF FISH AND F"SHERIES. 
cesophagus. Intestinal crura continued almost to the posterior end. 
Vitelline glands numerous, not only occupying the margins of the body 
as far as the middle of the neck, but also all the region behind the 
testes. Transverse duct with vitelline receptacle in front of the testes. 
Testes two, subgiobose, median, approximate with each other. Ovary 
globular, one-half the size of a testis, remote. Gyri of uterus few, 
situated in front of the testes. Genital apertures apposed in middle 
of neck. Bursa of penis long, smooth, cylindrical. Execretory vessel 
a median cecum, desisting in front of testes and opening in a posterior 
caudal pore. Length 6 mm., breadth 1.5 mm. 
This description is adapted, with a few changes, from Olsson, cited 
above. 
Habitat: Salmo mykiss, rectum. Heart Lake and Yellowstone Lake, 
July and August. 
A distomum which I have found frequently in the Rocky Mountain 
trout appears to be identical with D. lawreatum, a parasite which infests: 
several Kuropean fishes, e. g., Thymallus vulgaris, Coregonus oxyrhyn- 
chus, aud Salmo fario. 
The dimensions given by Dujardin for this species are: Length, 2 to 
3.35 mm.; breadth, 1 to 1.22 mm. 
My specimens, alcoholic, measure from 1.5 to 4 mm. in length and 
0.5 to 1.5 mm. in breadth. The length is in most cases three 
or four times the breadth. The diameter of the ventral sucker is 
about twice that of the oral sucker. The transverse diameter of the 
aperture of the ventral sucker is three times its axial diameter. The 
eggs are yellow, elliptical, usually collapsed in alcoholic specimens from 
0.07 to 0.085 mm. in Jength and 0.04 to 0.045 mm. in breadth. 
In life the color is yellowish-white; with transmitted light the eggs, 
which are large and not numerous, appear golden-brown. In the 
living specimens there appeared to be about five low, blunt papille on 
the dorsal half of the circumference of the oral sucker. Subsequent 
study revealed the number and disposition given above and in the 
sketches. This parasite was noticed on several occasions, but usually 
there were but few—a dozen or two—in each host. 
Detailed measurements of the specimen figured in Fig. 26 are as fol- 
lows: 
Millimeters. 
i B(s) 0g) 0 ie ae ae aerate pet IE Nt ae de ae cede ate oe a ah 3. 50 
Greatestrore adh 'wy.j5 is. Ne ee ee ae a Ll i pay ere 1.00 
Diameter of anterior sucker, interior, lateral ..............-..---- 0.17 
Diameter of anterior sucker, interior, axial.......-.....-.-------- “0. 15 
Diameter of anterior sucker, exterior: 5-222. 3.4222 2: seo seeee 0. 33 
Diameter, of ventral isucker; interior 355% 4s -eeen ies eee ese 0. 30 
Diameter of ventralisucker; exterior. 2:2 secces oes Se eee eee 0. 43 
a ee 
