76 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



thorax, a longer, narrower areola signifying a more spacious gill 

 chamber, a less pointed rostrum, and more tuberculate and sharper- 

 tipped chelae. 



Although a number of references have been made by us to the 

 associations between the epizoites and their hosts, it is not an omission 

 on our part that we have scarcely alluded to the relationships existing 

 between the branchiobdellids and the entocytherids. It seems 

 probable that the gill-inhabiting branchiobdellids, B. illuminatus and 

 C. branchiophila, probably have few contacts with the entocytherids 

 for, as pointed out, we have not encountered a single ostracod within 

 the gill chamber of the crayfish. Furthermore, contacts between Xg. 

 instabilius, the branchiobdellid that is almost confined to the chela of 

 the host, would also have little cause for encountering an ostracod, for 

 the latter has not been observed to inhabit the chelae of the hosts. 

 In contrast, most of the members of the genus Cambarincola, the two 

 members of Ankyrodrilus, P. alcicornus, and Xd. formosus do un- 

 doubtedly encounter the ostracods in the course of their moving about 

 the ventral part of the thoracic and abdominal areas of the crayfish. 

 Even though the methods of feeding of the branchiobdellids and 

 ostracods may be different, in view of the fact that they share the 

 same source of food scraped from the exoskeleton of the host, there 

 must be some degree of competition between them, however slight 

 the intensity of the competition might be. Furthermore, inasmuch as 

 several of the branchiobdellids are known to feed on other animals, 

 even other branchiobdellids, that dwell on the crayfish, it is a bit 

 surprising that there is no record of their having ingested an ento- 

 cytherid ostracod. One cannot help posing the question as to the 

 nature of the immunity of the entocytherids from the apparently 

 voracious appetite of their fellow epizoites! There are some data 

 that indicate that crayfishes heavily infested with branchiobdellids 

 seldom, if ever, have large numbers of ostracods. 



Two studies have been made elsewhere that are similar to that 

 undertaken here. Crawford (1959) treated the crayfishes and their 

 ostracod associates of Richland County, S.C., and Simonds 4 conducted 

 a study of the crayfishes and their ostracod and branchiobdellid 

 symbionts of the Hiwassee drainage system in Georgia, North Caro- 

 lina, and Tennessee. In both studies, only a single drainage system 

 was involved, the former dealing with the Santee river system and 

 the latter with a major tributary of the Tennessee-Ohio river system. 



Crawford found that within Richland Coimty there were 11 species 



4 Kenneth W. Simonds conducted this survey of the Hiwassee drainage system 

 in the late 1950s; however, a final report was not completed and no publications 

 have been derived from the survey except the descriptions of new species of 

 ostracods by Hobbs and Walton (1960, 1961). 



