PARASITIC FLATWORMS 375 



7 (6) Posterior disc with four large central hooks. Two pairs of eyes. 



Ancyrocephalus Creplin 1839. 



Anterior end bluntly triangular with two inconspicuous lobes on each side, but no distinct 

 cephahc lappets. Posterior disc bears four large, heavy hooks and clamp, and fourteen or 

 sixteen small marginal hooks of which two lie before and two behind the large hooks. Ovi- 

 parous. 



On the gills of many fresh-water fish. 

 _ Two species, determination doubtful, reported by Cooper from Ontario, Canada. On the 

 gills of young black bass. Also from rock bass and sunfish. 



• 



8 (3) Posterior organs multiple (two to many parted). Vagina double. 



Genito-intestinal canal present. 



Order Polyopisthocotylea Odhner . . 9 



Suckers at anterior end, if present, open into oral cavity. Posterior end with variable but 

 well-developed organs of attachment consisting of hooks and suckers grouped on a terminal 

 field or disc. 



9(12) With two oral suckers and with genital hooks 10 



10 (11) Posterior disc with eight, less often four (five) small peculiar sucking 



organs. 



Family Octocotylidae van Beneden and Hesse 1863. 



Elongate, flattened ectoparasitic trematodes. The posterior organ of attachment has — 

 usually in two parallel symmetrical rows — eight, more rarely four or six, small suckers braced 

 with a characteristic chitinous framework or armed with hooks. Extra hooks occur often on 

 the disc. Genital pore always armed with hooks. Eggs supplied with one or two long fila- 

 ments. On gills of marine and fresh-water fishes. 



These parasites are rare in fresh water yet no doubt other genera than the two cited here 

 do occur. The American representatives are not well known and only the first is more than 

 an accidental member of the fresh-water fauna. For this reason no effort has been made to 

 incorporate them in the key. 



Mazocraes Hermann 1782. 



One species, formerly known as Octohothrium sagittatum, is reported by Wright from the 

 sucker (Catostomus teres). 



Plectanocotyle Diesing 1850. 



Reported from the gills of Roccus americanus which enters fresh water to spawn so that this 

 parasite may be taken at tunes in that habitat. 



11 (10) Posterior disc with a large number of small suckers. 



Family Microcotylidae Taschenberg 1879. 



Elongate ectoparasitic trematodes with two small anterior suckers connected with the oral 

 cavity and with the posterior end expanded into a foot-like region bearing a multitude of 

 minute suckers. Eggs with large filaments at both poles. 



Body and posterior organ of attachment symmetrical. 



Microcotyle van Beneden and Hesse 1863. 



A genus parasitic on the gills of marine fishes. G. A. and W. G. MacCallum report three 

 species from the rock bass {Roccus lineatus) which ascends rivers along the Eastern Coast 

 for spawning. Hence these pirasites might be taken in fresh water, though no record of such 

 an occurrence has been found. 



12 (9) Anterior end pointed, without suckers or other special organs. 



Family Polystomidae van Beneden 1858 . . 13 



Elongate, flattened monogenetic trematodes with simple anterior end, and with prominent 

 adhesive disc at posterior end. Posterior disc with hooks and either two or six large powerful 

 suckers. Mouth subterminal, intestine triclad, often dendritic, with anastomoses. Male 

 genital pore and uterine orifice median, ventral, postpharyngeal. 



On body surface, gills, and in urinary bladder of amphibians; in pharynx and cloaca of rep- 

 tiles. 



