CONTRIBUTIONS TO AMERICAN HELMINTHOLOGY. 61 
The water-vascular system has a wide median stem, which con- 
tinues from the caudal pore half way to the ventral sucker, giving 
off in its course lateral branches, which communicate with the finer 
canals of the system. One of my specimens, which had been preserved 
in alcohol, was placed in a diluted carmine solution resembling 
Beale’s, but the fluid, instead of staining the tissues to any extent, 
entered the water-vascular stem and injected the subcuticular mesh- 
work, resulting in a beautiful preparation resembling the actual 
injections from which Blanchard’s figures of the water-vascular system 
in various Trematodes are taken." Rounded calcareous corpuscles oc- 
curred in great numbers in the median stem and its primary branches ; 
these seem to be especially abundant in immature Trematodes. 
On the ventral surface behind the acetabulum were several series 
of dark granular spots—perhaps the optical expression of cutaneous 
glands. 
2nD Sus-OrpER—MonocengaA. Van BEN. 
1.—OcronoTHRium sacitratum. F. §. Leuck. 
PLACOPLECTANUM SAGiITraTuM. Diesing. 
I possess several specimens of a worm from the gills of one of our 
fresh water fishes here, probably Catostomus teres, Le 8., which were, 
unfortunately, preserved without any label, and as to the babitat of 
which I am consequently uncertain. 
A comparison of Fig. 19, Pl. II., with Leuckart’s figure of Octo- 
bothrium sagittatum,” will show the great similarity between the 
appearanee of the worms. I cannot reconcile certain points in his 
description with what I have ascertained from these specimens ; but 
I propese to refer to these provisionally under this heading until I 
have access to a more satisfactory description of the worm living on 
the gills of the European brook trout, and until I secure fresh speci- 
mens.of the form taken here. 
The body is arrow-shaped, 6 mm. in length, with a greatest breadth 
of 1.5 mm. The body is separated by a marked constriction from 
the caudal disc, which is notched posteriorly, and has four suckers 
on each side of its ventral face. . 
The structure of these suckers is at variance with Leuckart’s de- 
scription. It is with great difficulty that one can succeed in getting 
@ satisfactory view of the chitinous framework, under a cover glass, 
19 Loe. cit., Pls. IX. and X. 
29 Zoolog. Bruchstiicke, III., Taf. V. 
