186 CLASS V. 



Sp. Monostoma faba SCHMALZ Tab. anatomiam entozoor. illustr. 1831, Tab. vi., 

 MIESCHER Beschreib. und Untersuch. der Monostoma bijugum, 1838, 4to. 

 In some species of the genus Fringilla this Entozoon 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 1 1 or 2 lines, and of the same breadth) in a little fluid. Monost. plicatum 

 CBEPLIN, Nov. Act. Acad. Gees. Leop. Car. xiv. 2, 1829, Tab. 52, in the 

 Bal. rostrata, &c. 

 Aspidogaster V. BAER. 



Tristoma Cuv., EUD. (Capsala Bosc, Phylline OKEN, Nitzschia 

 V. BAER). 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. DIESING Nov. Act. Acad. Leop. Car. TOM. xvm. i, Tab. I. (and 

 in French Monographic du genre Tristoma, Ann. des Sc. not. 2e Se"rie, IX. 

 Zool. 1838, pp. 77 89, PL I.) 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. Tristoma coccineum Cov. R. Ani. 

 1817, PI. xv. fig. 3, RUDOLPHI Entozoor. Synops. Tab. i. figs. 7, 8, BREMSER 

 Icon. Helm. Tab.x. figs. 12, 13, on the gills of Orthagoriscus mola and other 

 fishes. Trist. maculatum RUD. Voyage de LA PEROUSE iv. pp. 79, 80, 

 PI. 50, figs. 4, 5, on a species of Diodoti of California. Tristoma hamatum 

 RATHKE, Hirudo hippoglossi MUELL., BAST. Natuurk. Utisp. n. Tab. vin. 

 fig. xi. p. 152, Zool. danica, Tab. 54, figs, i 4 (infra), G. JOHNSTON Ann. 

 of Nat. Hist. i. 1838, p. 431, PI. xv. figs, i 3, RATHKE Nov. Act. Acad. 

 Leop. Car. XX. 1843, Beitrdge zur Fauna Norwegeris, pp. 238 242, 

 Tab. xn. figs. 9 n ; on the Halibut, &c. 



Polystoma RUD. 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 Hexacotyle DE LA ROCHE, Hexabothrium NORDMANN. 



Sp. Polystoma integerrimum RUD., BREMS. Icon. Helminth. Tab. x. figs. 25, 

 26 ; the urinary bladder of the frog, &c. 



Note. Genus Diplobothrium LEUCK. (Sp. Diplobothr. armatum in 

 the gills of Acipenser stellatus) is said to differ from Polystoma by 

 its six anterior acetabula; comp. LEUCKART Zoologische Bruchstucke 

 in. Freiburg, 1842, 4to. pp. 13 18, Tab. i. fig. 6. NORDMANN con- 

 siders these acetabula to be posterior, and does not separate the 

 species from the Polystomata, but calls it Hexacotyle elegans ; LA 

 MARCK Hist. nat. des ani. s. v. 2e edit. in. 1840, p. 600. 



