CONTRIBUTIONS TO AMERICAN HBLMINTHOLOGY. 61 



The water- vascular system has a wide median stem, whicli 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 Bianchard'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 Sub-Order — Monogenea. Van Ben. 



1. — OCTOBOTHRIUM SAGITTATUM. F. 8. LeUcTc. 



Placoflectanum SAGITTATUM. Diesing. 

 I possess several specimens of a worm from the gills of one of ^our 

 fresh water fishes here, probably Catostomus teres, Le S., which were, 

 unfortunately, preserved without any label, and as to the habitat of 

 which I am consequently uncertain. 



A comparison of Fig. 19, PL IL, with Leuckart's figure of Octo- 

 bothrium sagittatum,'"' will show the great similarity between the 

 appearance of the worms. I cannot reconcile certain points in his 

 description with what I have ascertained from these specimens ; but 

 I propose 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 

 ©f 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 

 :2j satisfactory view of the chitinous framework, under a cover glass^ 



i« Loc. cit.. Pis. IX. and X. 

 ^^OQlog. Brucbstiiclie, III., TaL V. 



