550 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 55. 



chances are all against their acquisition. We must be satisfied, there- 

 fore, with the morphological and structural details of the adults. 



The material for the present paper was derived from several sources. 

 The first and by far the most important one was the collection of the 

 United States National Museum, which included the new genus Peri- 

 plexis and the various species of Rebelula and Sphyrion. Then a 

 number of drawings have been generously placed at the author's dis- 

 posal, including a fine series by Dr. Richard Rathbun and two draw- 

 ings by J. H. Blake on Sphyrion lumpi, a second series by Rathbun 

 and a single drawing by Blake on Rebelula houvieri, a single drawing 

 by Blake of the new species, Rebelula gracilis^ and two drawings of 

 the new genus Periplexis by A. H. Baldwin. 



These drawings by Blake and Baldwin were made in 1882 and 1887, 

 and it is fortunate that they are finally to be published. 



The specimens of the genus Opimia were obtained by Dr. J. C. Mc- 

 Clendon from a shark at La JoUa, California, while those of both 

 species of the new genus Paeon were obtained by the present author 

 from sharks at Beaufort, North Carolina, while in the employ of the 

 United States Bureau of Fisheries. 



In the examination of specimens the same methods iiave been used 

 as in the Lernaedidae ; they were dehydrated in absolute alcohol and 

 cleared in clove oil, or better still in oil of wintergreen. In con- 

 sequence they became so transparent that the internal anatomy was 

 visible in all its details. The pigmy males, after such treatment, were 

 mounted in toto in Canada balsam on culture slides and are preserved 

 in this manner. 



Serial sections have also been made of one of the partially developed 

 females of Sphyrion lumpi, thus supplementing the work with the 

 cleared specimens. 



As here constituted the family is made up of six genera, two of 

 which, Periplexis and Paeon, are new to science, and 14 species, of 

 which the females of five are new, as well as all the males. 



HISTORICAL. 



Quoy and Gaimard seem to have been the first to discover any of 

 the species belonging to this family. They figured and described in 

 the report of Freycinet's voyage around the world (1824) a parasite 

 which they referred to the genus Ohondr acanthus, and to which they 

 gave the French name "lisse." Cuvier (1830) recognized that this 

 species did not belong to the genus Ohondr acanthus, and with it as a 

 type he established the new genus Sphyrion (vol. 3, p. 257). Guerin 

 (1829-1844) translated the French name " lisse " into the Latin 

 equivalent laevigatus (vol. 2, pi. 9, fig, 4), but added nothing further 

 to the description. 



