126 REPORTS 01^ INVESTIGATIONS AND PROJECTS. 



cestodes of the Tortugas selachians I have found that they compare favor- 

 ably, both in number of species and of individuals, with those of the northern 

 selachians. 



Adult cestodes were found in all of the selachians examined. An interest- 

 ing case is afforded by the spotted stingray, which was examined for the 

 first time this summer. Two genera, OnchobotJirium and Tylocephaluiii, 

 were found in this ray. The latter genus was established by me in 1890 

 (Report U. S. Fish Commission for 1887, pp. 806-809, pi. ix, figs. 5-9), and 

 was based on a single specimen. This is a practice which, as a rule, has 

 little to commend it. In this case, however, the scolex was so characteristic 

 that there was no doubt of its unique systematic position. The original spec- 

 imen came from the cow-nosed ray {Rhino pt era bonasiis) collected at Woods 

 Hole in 1887. I have had but few opportunities to examine the eagle-rays, 

 and none were seen by me between the years 1887 and 1908 except three in 

 1889. The genus Tyloccphalnm remained without any other justification 

 than the single specimen collected in 1887 at Woods Hole. Two specimens 

 belonging to this genus were found in one of the spotted stingrays. They 

 are adult, with mature segments, and should furnish important additional 

 anatomical data to our knowledge of this singular cestode. Incidentally, it 

 illustrates an important principle in the distribution of entozoa. Some genera 

 of cestodes are intimately associated with, and often restricted to, either a 

 single genus or a family. This is particularly true for the adult stages. 

 There is thus suggested an interesting series of problems whose solution will 

 rest not only on the working out of the life history of many of the cestodes, 

 but also on a study of the comparative physiology of the various hosts. 



Treuiatodes. — Representatives of this order were found in 21 of the 32 

 species of fish examined. Twenty-eight species, mostly distomes, were added 

 to the list of the past two years. This number includes those new to the re- 

 gion and those found in a new habitat. Among the former, as of especial 

 interest, may be mentioned an example of Aspidogastcr found in the porgy 

 (Calamus calamus), and a species of UdoncUa, a number of which, together 

 with their ova, were found attached to the bodies of 2 parasitic copepods 

 in the mouth of a gray snapper {Neomccnis griseits). 



I have made a preliminary examination of the distomes collected in the 

 summers of 1906 and 1907, with a view to determining their systematic rela- 

 tions. In this examination I have made use of Professor Pratt's Synopsis of 

 North American Trematodes. That I fail to find a satisfactory abiding place 

 for the majority of these Tortugas distomes is not the fault of the excellent 

 Synopsis, but is to be charged rather to the very large number of genera, 

 made possible, and even necessary, by the criteria which have been adopted 

 by modern helminthologists in the dismemberment of the old genus Dis- 

 tomum. 



Thus the best that I am able to do at present is to report the following list 

 of genera_ which are either near to, or suggested by, specimens in the collec- 

 tion. This list will be lengthened considerablv when the distomes collected 

 in 1908 are added. 



Astiotrema. Halicometra (4 species). Opisthorchis. 



Azzygia. _ Halipcgus (2 species). Psilostomuni (2 species). 



Cathaenasia. Hemiunis (2 species). Progonns. 



Derogenes (4 species). Lecitliaster. Pyelostomum. 



Gasterostomum (2 species). Lecithocladium. Stephanochasmus. 



G ossidium. Lepidophyllum. Stvphlodora. 



Glyphicephalnm. Liopvge. Tcrgestia. 



Gymnophallus. Microcotvle. 



