No. 404.] MORTH-AMERICAN INVERTEBRATES. 651 
. and bears two hooks; body elongate: on 
gills of Mustelus 
Erpocotyle v. Ben. et Hesse (Fig. 24) 
£ Suckers stalked ; terminal projection narrow, 
with four hooks ; body attenuated : on gills 
of Accipenser 
Diplobothrium F. S. Leuck. (Fig. 25) 
£g The terminal projection is bifid at its extremity, 
each half bearing a small sucker; body 
elongate : on gills of selachians 
Onchocotyle Dies. (Fig. 26) 
d,. Posterior region with four to eight large suckers ; paired 
anterior suckers present . Subfamily II. Octocotyline 
e, Posterior region with four (five) suckers. 
f, Posterior region with two pairs of suckers at the 
end of long stalks ; body elongate: on gills of 
marine fishes 
Platycotyle v. Ben. et Hesse (Fig. 27) 
Ja Posterior region with four suckers in a lateral, 
longitudinal row, to which may be added a fifth 
smaller sucker on the opposite side ; body elon- 
gate and asymmetrical : on gills of marine fishes 
(Scomber). . . Pleurocotyle Gerv. (Fig. 28) 
e, Posterior region with six (three pairs) suckers. 
fı- Body elongate ; posterior region with the six suckers 
bears at its posterior end a tail-like projection, at 
the extremity of which is a single sucker: on 
gills of marine fishes 
Phyllocotyle v. Ben. et Hesse (Fig. 29) 
f, Body either elongate or broadly elliptical ; suckers 
on the broad posterior margin, in the median 
line of which, between the median suckers, a pair 
of hooks on a short projection may or may not 
be present : on gills of marine fishes 
Plectanocotyle, Dies. (Fig. 30) 
e, Posterior region with eight (four pairs) suckers. 
f, Individuals fused together, v-shaped, in pairs ; body 
elongate; posterior suckers sessile : on gills of 
fresh-water fishes Diplozoón v. Nordm. (Fig. 31) 
f; Individuals not fused together in pairs. 
gy Body asymmetrical, elongate, composed of two 
equal portions, which form an angle with 
each other; posterior suckers sessile: on 
gills of Lichia : 
Vallisia Par. et. Per. (Fig. 32) 
