654 
A 
THE AMERICAN NATURALIST. [VoL. XXXIV. 
e, Two short anterior projections ; posterior disk with 
usually sixteen marginal hooks ; no eyes 
Gyrodactylus v. Nordm. (Fig. 43) 
e, Four short anterior projections ; posterior disk with 
usually fourteen marginal hooks ; four eyes 
Dactylogyrus Dies. (Fig. 44) 
. No tentacle-like anterior projections. 
£€,. A pair of anterior suckers present; posterior end 
extended transversely, with four marginal hooks: on 
the gills of marine fishes 
Diplectanum Dies. (Fig. 45) 
e» No anterior suckers present. 
Jı Posterior region with four large central hooks. 
gı- Body contracted posteriorly; posterior disk 
with a number (12-16) of small marginal 
hooks; anterior end triangular, with four 
slight projections : usually on gills of fresh- 
water fishes . Tetraonchus Dies. (Fig. 46) 
£» Body elongate ; posterior region trilobed, with 
twelve minute marginal hooks : on gills of 
Torpedo . Amphibdella Chatin (Fig. 47) 
£y. Posterior disk stalked, with lobed margin and 
no marginal hooks : on gills of Coregonus 
Dactylodiscus Ols. (Fig. 48) 
J, Posterior region with no large central hooks or with 
ut one. 
£, Broad, Wea membrane-like projection at 
. anterior end ; posterior disk terminal, either 
unarmed, with minute hooks, or with a single 
large central hook ; body elongate, cylindri- 
cal : on gills of marine fishes 
Calceostoma v. Ben. (Fig. 49) 
£» A pair of glandular areas at anterior end ; pos 
terior disk terminal, irregularly elliptical, 
with minute hooks in center; a prominent 
glandular projection in middle of right side 
of body: on eggs of a fresh-water fish in 
Brazil . . Fridericianella Brds. (Fig. 5°) 
£y Two sucker-like depressions at anterior end ; 
posterior disk without hooks: on gills o 
Pagrus . . . . Anoplodiscus Sonsino. 
