566 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 17. 



States Bureau of Fisheries. For these excellent advantages the author 

 is indebted to the courtesy of the Hon. George M. Bowers, former 

 United States Commissioner of Fisheries. 



The internal anatomy has been derived partly from the study of 

 living specimens at each of the above locahties, and partly from 

 serial sections made in the laboratory of Johns Hopkins University, 

 as noted in the ninth paper above mentioned. 



A number of specimens, including several of the new species, were 

 collected by Dr. Edwin Linton during his investigations on the 

 cestode and trematode parasites of fishes, and were generously turned 

 over by him to the present author. These specimens are always 

 excellently preserved and have proved of great value in the present 

 study. 



Several years ago Dr. R. R. Gurley, at that time in the employ of 

 the United States Bureau of Fisheries, collected in manuscript form 

 all the available data regarding copepods parasitic upon our North 

 American freshwater fishes. These notes have been placed at the 

 author's disposal, and as they included complete translations of 

 everything written on North American species by foreign authors 

 they have proved extremely valuable. Acknowledgment is made in 

 the text whenever these notes have been incorporated. 



Dr. Nathan Fasten, of the Department of Zoology at the Univer- 

 sity of Wisconsin, has recently published three excellent papers on 

 the habits and development of a species of this family which infests 

 the common brook trout. At the author's request Dr. Fasten very 

 kindly loaned mounted specimens of the copepodid larvae and male 

 of this species, Salmincola edwardsii, which have been of much use for 

 study and comparison. 



As here constituted the family includes 23 genera and 136 species, 

 of which 12 genera and 21 species are new to science. 



In addition there are several other genera and species vvhich at one 



time or another have been included in this famil}^, but which must be 



regarded as synonyms or as not sufficiently well established to be 



definitely located. 



ECOLOGY. 



Wherever the Lernaeopodidae may be placed in any scheme of 

 classification, all authors will agree that they are fixed parasites and 

 extremely degenerate. Consequently we should look for marked 

 sexual dimorphism, a partial or total loss of the powers of locomotion, 

 and a corresponding complexity in the means of prehension. And 

 we find these abundantly exemplified. 



Sexual dimorphism. — The differences between the sexes manifest 

 themselves not only in an enormous disparity in size, coupled with 

 a corresponding dissimilarity in the structure of the body and its 

 appendages, but also in the methods and extent of prehension and 



