570 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.51. 



to be longer and more slender, and the abdomen is distinctly notched 

 at the tip and usually shows no indication of its component parts. 



A series of over 20 of these crustaceans was obtained from speci- 

 mens of Synalpheus longicarpus (Herrick) picked out of a large sponge 

 dredged by the Bureau of Fisheries Steamer Fish Hawk from a depth 

 of about 10 fathoms. About 5 per cent of the slirimps bore this para- 

 site and another 5 per cent had a branchial parasite (Synsynella 

 deformans, new species) . No case was found in which both kinds were 

 present in the same individual. The parasites attach themselves to 

 the under surface of the abdomen of their host, to whose swimmerets 

 they cling with their prehensile feet. So strong is the hold of the 

 females that unless great care is exercised in removing them their legs 

 are invariably broken off and left beliind. The ventral surface of the 

 parasite is uppermost and its head is turned toward the tail of its host. 

 In addition to the attaclmient by the feet, there appears to be a sort 

 of pedicel extending from the soft interarticular membrane of the 

 shrimp to the mouth of the parasite, but it is so completely liidden 

 that I have not been able to satisfy myself as to its nature. All the 

 females are apparently mature and are swollen with eggs. About half 

 of the specimens are accompanied by males, but the latter are not 

 found on the females as is usual in the parasitic isopods, but are to be 

 found cHnguig to bases of the swimmerets or the last pair of walking 

 legs of the host, immediately above the position occupied by their 

 mate. In one case a small male was found within the egg pouch of a 

 female; it is much smaller than the free males, its antennae and legs 

 are much reduced in size, its abdomen is longer, turned to one side 

 at its extremity and undulate along the margins, and the eyes and 

 antennules are not discernible. Whether this is merely an immature 

 male or a complemental male somewhat similar to those described 

 by Bonnier in Grapsicepoji edwardsii I am unable to determine. 



The striking difference between this species and P. ohdominalis is 

 the presence in the adult female of P. suhcaudalis of five well-developed 

 legs on the long side of the body. It is stated by Sars that the imma- 

 ture female of P. ahdominalis has fom- such legs, the last three of 

 which are reduced at maturity to mere vestiges. It may be that the 

 small size of the host of P. suhcaudalis has made the parasite so 

 stunted that it has retained some of its immature characteristics, but 

 it appears more probable that we are deaUng \\dth a more primitive 

 species, which retains its ancestral characteristics. 



With the exception of Spence Bates's record for the Philippine 

 Islands, P. ahdominalis has been reported only from locahties much 

 farther north than Beaufort, and it appears to be most conunon in 

 Arctic waters. The range of P. suhcaudalis is probably a much more 

 southern one, for its host belongs to a subfamily the members of which 

 are practically all tropical and subtropical in their distribution. 



