, 
60 CONTRIBUTIONS TO AMERICAN HELMINTHOLOGY. 
5.—DIstomuM GRACILE. Diesing. 
CLINOSTOMUM GRACILE. Leidy. 
This worm was first described by Dr. Leidy,’® who regarded it as 
generically different from Distomum. He records it from the in- 
testines of a Pike, and from cysts in the gills, fins and muscles of 
Pomotis vulgaris (auritus), Giinther. I have found the same worm 
in cysts on the branchiostegal membrane and anterior fins of Perca 
flavescens, Cuv. This species appears to me to belong to the same 
group as D. heterostomum and D. dimorphum, from the structure of 
the anterior end, and of the ventral sucker. In a specimen of 6.45 
mm. in length, with a greatest breadth of 1.8 mm. across, the mouth 
sucker measures 0.338 mm. across, and the prominent border which 
surrounds it 0.975 mm. The large ventral sucker (0.91 mm.) is situ- 
ated in the middle of a constriction dividing the neck from the 
body, and has a triangular aperture. Its cavity is lessened by three 
triangular tongues, which project into it so as nearly to meet each 
other. The anterior of these points with its apex backwards; all 
are formed chiefly of radial fibres, and they must undoubtedly 
increase the efficiency of the sucking apparatus very considerably. 
The species of Distomum which have been found included in cysts 
are either fully mature (D. agamos, V. Linst.,"7 D. Okenii, Koll., 
D. crassicolle, R. [Pontallié]), or have only one part of the sexual 
apparatus ripe (D. hystrix., Dujard., the testes’), or are finally quite 
immature. In the last category fall D. annuligerum, Nordm., D. 
diffusocalciferum, Gastaldi, D, dimorphum, Diesing, and, as I believe, 
D. gracile. No mention of generative organs is made in Leidy’s 
description, and I have failed to detect any trace of such. The Sun- 
fish and Perch can consequently hardly be regarded as the definitive 
hosts of this worm. Probably the sexually mature worm is to be 
sought for in the intestine of some larger fish (Pike?) or piscivorous 
bird. In the latter case, the relationship between the immature 
and mature form would resemble the two forms of D. dimorphum 
described by Diesing. 
The intestinal coeca are large, and extend nearly to the posterior 
end; the contents are yellowish-brown, and include some lozenge- 
shaped concretions. 
16 Proc. Ac. Sci. Phil. VIII., p. 45. 
17 Trosch. Arch. XXXVIII., B. I., p. 1, f. 
18 Olsson, Lund’s Univers. Arsskr, IV., p. 52. 
