No. 431.] NWORTH-AMERICAN INVERTEBRATES. 891 
B, Either a large ventral sucking disk or a mid-ventral row of suck- 
ers present; no oral sucker; intestine not bifurcate (except 
possibly Aspidocotylus) . . . Aspidocotylea Mont. 
B,. Either one or two or, in a few cases, more than two median 
suckers present; an oral sucker invariably present (except 
Gasterostomum) ; intestine, except in rare cases, bifurcate 
Malacocotylea Mont. 
KEY TO THE GENERA OF THE SUBORDER ASPIDOCOTYLEA AND THE 
FAMILY ASPIDOBOTHRID/E. 
4,. A single mid-ventral row of suckers present, extending nearly or quite 
the length of the body, which is elongate and cylindrical. 
&,. Suckers contiguous and confluent, on a distinct ridge of the body ; 
one testis: in gall bladder of Chimera 
Macraspis Olss. (Fig. 1) (55, 66)' 
b, Suckers not contiguous and not on a ridge ; two testes : in gall pas- 
sages of skates (as adults) and in cysts in the end-intestine of 
lobsters (as larva) . Stichocotyle Cunn. (Fig. 2) (62, 68, 66) 
a, Very large circular or oval sucking disk present. 
b,. Sucking disk circular, containing a number of small round sucking 
pits; intestine possibly bifurcate: in the intestine of fresh-water 
fsh . . . . . . . Aspidocotylus Dies. (Fig. 3) (58, 66) 
5,  Sucking disk circular or elliptical and containing three or four lon- 
gitudinal rows of more or less rectangular depressions separated 
from one another by ridges. 
¢,. Sucking disk with three rows of depressions. 
d,. Sucking disk irregularly circular or elliptical, with crenulate 
border and with transversely elongated depressions; one 
testis. 
e, Number of depressions about twenty-five; marginal 
sense organs and eyes absent : in intestine of cheloni- 
ans . . . .  Platyaspis Mont. (Fig. 4) (58, 66) 
e,. Number of depressions about twenty-nine; twenty 
marginal sense organs and two eyes present: in 
mantle chamber of fresh-water mussels 
Cotylaspis Leidy (Fig. 5) (22. 17; 66) 
d, Sucking disk elliptical, with very long transversely elongated 
median depressions and small round lateral ones; two 
testes; marginal sense organs: in the intestine of fish 
Cotylogaster Mont. (Fig. 6) (58, 66) 
1 The numbers in parentheses following the name of a genus or a species refer 
to the publications in the bibliography in which descriptions of it may be 
found. 
