Monogenetic Trematodes, I — Yamaguti 
83 
clamps of four pairs, subequal, of Discocotyle 
type, bivalved, sessile. Vagina double. 
Pseudodisco cotyla n. g. 
GENERIC DIAGNOSIS: Discocotylidae, Pseudo- 
discocotylinae. Body tapering anteriorly; opis- 
thohaptor two-lobed, with a median pair of 
larval hooklets posteriorly and four pairs of sub- 
equal bivalved clamps; clamp skeleton consisting 
of two pairs of slender, un jointed, lateral arms, 
a median spring and a pair of incurved basal 
rods. Prohaptoral oral sucker septate. Esopha- 
gus bifurcating posterior to genital pore; ceca 
slightly diverticulate, not united posteriorly. 
Testes very numerous, occupying nearly whole 
postovarian intercecal field. Armed bulbus cirri 
present. Genital atrium armed. Genital pore 
prebifurcal. Ovary turned back on itself, with its 
distal end directed backwards. Genito-intestinal 
duct present. Shell gland complex between two 
submedian groups of testes. Eggs elliptical, large, 
with convoluted filament at each pole. Vaginae 
lined with corrugated cuticle, situated ventrally 
near lateral margins of body at a level a little 
behind genital pore; vaginal duct not traced. 
Vitellaria extending along entire intestinal limbs 
posterior to vaginae; vitelline reservoir Y-shaped, 
with its arms distended with sperm at its an- 
terior end in form of oval sac. Gill parasites of 
marine teleosts. 
TYPE SPECIES: P. opakapaka n. sp. on gills of 
Pristipomoides microlopis and Aphareus ruti- 
lans; Hawaii. 
14. Allopseudaxinoides euthynni n. g., n. sp. 
Fig- 15 
HABITAT: Gills of Euthynnus yaito (local 
name "kawakawa” ) ; Hawaii. 
HOLOTYPE: U. S. Nat. Mus. Helm. Coll., S.Y. 
No. 14. 
DESCRIPTION (based on 12 whole mounts): 
Body large, 5-8 mm long from head end to tip 
of caudal appendage, markedly tapered in head 
and esophageal regions, widest (2.9-5. 5 mm) 
at opisthohaptor which extends obliquely along 
the posterior end of the body proper. Opistho- 
haptor unilateral, bearing a row of 13-15 clamps 
and a prominent digitiform caudal appendage 
which is provided at its blunt end with two 
pairs of anchors; outer anchor 47-5 3/x long, 
inner one 22-2 5 /a long. Clamp bivalved, 0.15- 
0.3 mm in diameter; median spring U-shaped, 
with rounded ends, consisting of sclerotized me- 
dian piece and parallel-sided muscular flange 
which appears as a winglike lateral extension of 
the median piece in optical section; the dorsal 
valve of clamp is supported by a pair of arcuate 
lateral sclerites meeting at tip of valve and 
curved medially at base; the ventral valve is sup- 
ported by a pair of apically slightly curved scle- 
rites meeting in the median line and articulating 
at the base with the dorsal sclerites at the angle 
where they bend medially. Beneath the apical 
ends of the dorsal and ventral sclerites are paired 
sclerotized thickenings of the median apical mar- 
gins of the capsules of the dorsal and ventral 
valves. Head rounded, 0.13-0.17 mm wide; 
mouth ventroterminal. Paired oral sucker 25- 
35 X 30-43g; pharynx pyriform, 40-70 X 30- 
43 g, sometimes protruding into buccal cavity. 
Esophagus simple, 0.38-1.05 mm long; bifurcat- 
ing a short distance posterior to genital atrium; 
intestinal limbs with short inner and longer 
outer branches, terminating in distal portion of 
opisthohaptor, the right limb reaching to base 
of caudal appendage. 
Testes up to about 20 in number, irregular in 
shape, extending in interintestinal field from 
preovarian area to postovarian area, passing in 
one row on left side of ovary. Vas deferens 
narrow, almost straight dorsal to uterus. Cirrus 
forming a bulb surrounded by fine circular 
muscle fibers, produced forward into a cuticu- 
larized short cylinder tipped with a circular row 
of delicate spiniform structures which projects 
into the lumen of the genital atrium. Genital 
atrium spherical, 42-45 /x in diameter, with thick 
wall of radial muscle fibers, armed inside with 
a corona of over a dozen ( 14-24? ) spines 20- 
25 fi long whose bifid tips are curved inwards; 
these spines are supported at the base by an- 
other corona of stumpy denticles. Genital pore 
midventral, 0.25-0.6 mm from head end. 
Ovary 1.3-1. 8 X 0.15-0.4 mm, turned back 
on itself in midregion of body, with both ends 
directed backwards. Genito-intestinal duct cross- 
ing proximal and distal ends of ovary and open- 
ing into right intestinal limb. Uterus midventral; 
eggs elliptical, 0.12-0.2 mm long by 70 /x wide, 
with polar filament 0.07-0.14 mm long at each 
pole. Vitellaria co-extensive with intestine and 
its branches. Vitelline reservoir Y-shaped; its 
