2 PROCEEDINGS OF THE NATIONAL MUSEUM vol.88 



Much difficulty is experienced when one attempts to identify alco- 

 holic or formalin specimens of these soft-bodied forms, which not 

 only assume diverse contraction shapes but may vary considerably 

 in the size and relative proportions and positions of parts with the 

 age of the individuals. No special search was made for monogenetic 

 forms. Such as were found had usually been washed off the gills 

 while preparing the viscera for examination. In the summers of 1912 

 to 1927 such helminths from the gills and skin of fishes as were met 

 with were turned over to Dr. G. A. MacCallum, who was giving espe- 

 cial consideration to the monogenetic trematodes. 



The author is under obligations to Drs. H. W. Manter and H. W. 

 Stunkard for information that has prevented some duplication of 

 names as a result of work carried on by them on forms noted in this 

 report. 



The invaluable index catalog of Stiles and Hassall ^ renders it un- 

 necessary, in most cases, to cite literature prior to 1908. For the 

 convenience of future investigators, however, frequent references have 

 been given to earlier papers of the author, on trematodes from the 

 Woods Hole region. 



The names of fishes used in this report are those given in the check 

 list of Jordan, Evermann, and Clark.^ 



Order MONOGENEA van Beneden, 1858 



Suborder MONOPISTHOCOTYLEA Odhner, 1912 



Family GYRODACTYLIDAE van Beneden and Hesse, 1863 



Subfamily Gyrodactylinae Monticelli, 1892 



Genus GYRODACTYLUS Nordmann, 1832 



GYRODACTYLUS species 



Plate 14, Figure 158 



On August 6, 1911, Dr. R. A. Spaeth called my attention to certain 

 small monogenetic trematodes (U.S.N.M. No. 8142) on the scales of 

 the common killifish {Fundulus heteroclltus) . Later, on August 18, 

 Dr. C. W. Hahn, who was examining killifishes for sporidia, reported 

 these worms abundant on fishes he had been examining. 



Measurements, life: Length, 0.5 mm.; breadth, anterior, 0.05 mm.; 

 maximum, a little back of middle, 0.12 mm.; length of large hooks, 



^ Index-catalogue of medical and veterinary zoology. Subjects : Trematodes and trema- 

 tode diseases. U. S. Hyg. Lab. Bull. 37, 401 pp., 1908. 



s Check list of the fishes and flshlike vertebrates of North and Middle America north of 

 the northern boundary of Venezuela and Colombia. Rep. TJ. S. Comm. Fish. 1928, pt. 2, 

 670 pp., 1930. 



