186 CLASS V. 
Sp. Monostoma faba Scumauz Tab. anatomiam entozoor. illustr. 1831, Tab. VI., 
Mirscourer Beschreib. und Untersuch. der Monostoma bijugum, 1838, 4to. 
In some species of the genus Fringilla this Hntozoon has been found 
occasionally in membraneous sacs immediately beneath the skin, usually of 
the abdomen, back, or even of the thighs, and resembling round elastic 
tumours of the size of a pea. In every sac lie two worms (of the length 
of 13 or 2 lines, and of the same breadth) in a little fluid. Monost. plicatum 
Crepuin, Nov. Act. Acad. Cas. Leop. Car. XIv. 2, 1829, Tab. 52, in the 
Bal. rostrata, &e. 
Aspidogaster V. BAER. 
Tristoma Cuy., Rup. (Capsala Bosc, Phylline Onn, Nitzschia 
V. Barr). Body depressed. Mouth anterior between two acetabula 
simple, marginal; third acetabulum posterior, large, circular, and 
marked internally with projecting lines; these are disposed fre- 
quently in the form of a wheel or a star. 
Comp. Dresine Nov. Act. Acad. Leop. Car, Tom. Xvitt. 1, Tab. 1. (and 
in French Monographie du genre Tristoma, Ann. des Sc. nat. 2e Série, Tx. 
Zool. 1838, pp. 77—89g, Pl. 1.) These worms live on the gills or on the 
skin of different fishes, and thus are not entozoa in the proper sense of the 
term, but rather external parasites. Sp. Ziristoma coccineum Cuv. R. Ani. 
1817, Pl. xv. fig. 3, RupotPur Lntozoor. Synops. Tab. 1. figs. 7, 8, BREMSER 
Icon. Helm. Tab.x. figs. 12, 13, on the gills of Orthagoriscus mola and other 
fishes. T'rist. maculatum Rup. Voyage de LA PEROUSE IV. pp. 79, 80, 
Pl. 50, figs. 4, 5, on a species of Diodon of California.—Tristoma hamatum 
RatuKeE, Hirudo hippoglossi Muntu., Bast. Natuurk. Uitsp. 1. Tab. vit. 
fig. XI. p. 152, Zool. danica, Tab. 54, figs. 1—4 (infra), G. JOHNSTON Ann, 
of Nat. Hist. 1. 1838, p. 431, Pl. xv. figs. 1—3, Ratuxe Nov. Act. Acad. 
Leop. Car. Xx. 1843, Beitrdge zu Fauna Norwegen’s, pp. 238—242, 
Tab. xu. figs. g—11; on the Halibut, &e. 
Polystoma Rup. Body roundish or depressed, narrowed for- 
wards, with terminal mouth; in the posterior dilated portion fur- 
nished with six acetabula muscular, supported by horny parts, 
uncinate. 
Genera Heaxacotyle Dr tA Rocun, Hexabothrium NorpMANN. 
Sp. Polystoma integerrimum Ruv., Brems. Icon. Helminth. Tab. x. figs. 25, 
26; the urinary bladder of the frog, &e. 
Note.—Genus Diplobothrium Lruck. (Sp. Diplobothr. armatum in 
the gills of Acipenser stellatus) is said to differ from Polystoma by 
its six anterior acetabula; comp. Lruckart Zoologische Bruchstiicke 
m1. Freiburg, 1842, 4to. pp. 13—18, Tab. 1. fig. 6. NorDMANN con- 
siders these acetabula to be posterior, and does not separate the 
species from the Polystomata, but calls it Heaacotyle elegans; La 
Marck Hist. nat. des ant. s.v. 2e edit. 111. 1840, p. 600. 
