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Sa PROCEEDINGS OF THE NATIONAL MUSEUM. 99 
_ terior end. The pharnyx was 0.1 millimeter in length, and 0.06 milli- 
meter in breadth, its anterior end 0.03 millimeter back of the oral aper- 
ture. 
The ova were few, about nine were counted, and were relatively 
large, 0.09 millimeter in length. Several of them were observed to be 
undergoing segmentation (Figs. 39 and 40). 
The ovary is situated in front of the testes, and near the anterior one; 
the vitellaria are voluminous, occupying the posterior part of the body 
behind the testes and the margins of the body nearly as far forward as 
the ventral sucker. 
HABITAT: Oedemia americana, intestines, Yellowstone Lake, August, 
1890. 
CESTODA. 
Dibothrium cordiceps Leidy. 
(Pl. vi, Fig. 45.) 
Larval (encysted) stage in Salmo mykiss. 
Leidy, Hayden’s Report on Geol, of Montana and Adjacent Territory, 1871, p. 381, 382. 
Linton, Bulletin U. S. Fish Commission, 1889, Vol. 1x, pp. 65-79. Pl. XXIII-XxXVII, 
Adult stage, in Pelecanus erythr orhynchus. 
Linton, Bulletin U. S. Fish Commission, 1889, Vol. 1x, pp. 337-358. Pl. exvil-cxrx. 
I have referred to this species a small lot of immature specimens, be- 
longing to the genus Dibothrium, obtained from the intestine of the 
California Gull (Larus californicus), Yellowstone Lake, August, 1890. 
Five specimens were found in one gull and one in another. 
The specimens have the following characters: Bothria lateral; body 
rather thick, subecylindrical in front, compressed elsewhere, tapering 
posteriorly, crossed by exceedingly fine strix. 
The dimensions of an average specimen are as follows: 
Millimeters. 
Men SUH tae cow esac Snare saree te cle clas oe ee eiioeees 7.00 
Wiameenomheads 2252. ses 5:22 obasunassewaasae ee aeeaee .o2 
Diameter of body, anterior lateral..................-.. . 65 
Diameter of body, anterior marginal........---....-... .40 
Diameter near posterior end....-....-.---+--.-.--26--% . 20 
There is no indication of reproductive organs. 
The species D. cordiceps is not excluded by any characters yet de- 
veloped in these specimens. Satisfactory identification, however, is 
always difficult in forms like these, which may assume such diverse 
shapes with different degrees of contraction. 
On account of the small size and immature condition of these speci- 
mens it may be inferred that they had not been in the intestine of the 
gull very long. It does not follow, therefore, that they would reach 
maturity in this host. So that even if the specimens have been cor- 
rectly identified in this case it can not be said positively that the gull 
is a proper final host of D. cordiceps. 
