648 THE AMERICAN NATURALIST.  [Vou. XXXIV. 
body ; 2 pairs testes ; sucker-like pit near mouth ; mouth with pro- 
boscis ; pharynx distinct . . . Actinodactylella Hasw. (Fig. 3) 
4, Body without four to twelve finger-like tentacles. 
6,. Body usually broad and flattened, sometimes elongate or cylindrical, 
with a single ventral or terminal posterior sucking disk, usually 
of large size and armed with hooks and with or without radial 
ridges ; paired anterior suckers either present or not. 
c,. Paired anterior suckers present or in their place a pair of pro- 
jections (or a pair of glandular depressions, Goto) 
Family II. Tristomide 
d,. Body elliptical or circular and flattened. 
e, Sucking disk large, with or without radial ridges, and 
either sessile or with short stalk ; genital pores in 
most cases on left . . Subfamily I. Tristominz 
fi: Genital pores on left. 
gı Sucking disk without radial ridges ; four eyes. 
A,» Anterior suckers present. . 
í. Body elongate; sucking disk terminal, 
with (or without, Linton) numerous 
minute hooks ; testes numerous : 1n 
branchial cavity of marine fishes 
Nitzschia v. Baer (Fig. 4) 
Z, Body elliptical ; sucking disk ventral, 
with three (two, Linton) pairs of 
hooks of unequal size and often with 
papilla ; two testes: on the skin of 
marine fishes 
Epibdella Blain. (Fig. 5) 
h,. Anterior suckers not present, in their place 
a paired membrane ; sucking disk with 
two pairs of hooks ; two testes: on the 
skin of marine fishes 
Phyllonella v. Baer (Fig. 6) 
£» Sucking disk with radial ridges ; eyes present 
or not ; anterior suckers present. 
A. Sucking disk with nine radial ridges and 
two large hooks; two testes ; four eyes ; 
body elliptical : on gills of marine fishes 
^  . Tróchopus Dies. (Fig. 7) 
ha. Sucking disk with four to six faintly marked 
radial ridges and two or three pairs of 
hooks; two testes; four eyes; body 
elongate : on skin of marine fishes 
Placunella v. Ben. et Hesse (Fig. 8) 
A, Sucking disk with seven radial ridges: 
