THE PARASITIC ISOPOD LEIDYA DISTORTA (LEIDY) 
FOUND ON A NEW HOST. 
By Harrinr Riciarpson, 
Collaborator, Division of Marine Invertebrates, U. S. National Museum. 
~ 
Prof. A. E. Verrill has recently sent me specimens from the Ber- 
muda Islands of Pachygrapsus transversus (Gibbes), infested with 
an Isopod parasite. The parasite is located in the branchial cavity 
of the host. On examination the Isopod was found to be Letdya dis- 
torta (Leidy), heretofore recorded as parasitic on Uca pugilator 
(Bosc). This genus and species is therefore not confined to one 
genus and species of host. 
The species found by Fritz Mueller in the branchial cavity of a 
Grapsoid Pachygrapsus transversus (Gibbes), from the coast of 
Brazil, is probably this species and genus, and not Gvrapsicepon 
fritz, the nominal species of Giard and Bonnier.‘ 
Because Grapsicepon edwardsi was found on a Grapsoid, Planes 
minutus, according to the theory advanced by these authors the para- 
site of another Grapsoid of the same family, Pachygrapsus trans- 
versus, would naturally be a Grapsicepon. The facts prove, however, 
that this is not always the case, in this instance as in other parasitic 
Isopod genera before cited. 
Leidya is found parasitic on both Uca and Pachygrapsus, two 
widely separated genera of hosts belonging to different families. 
As no descriptions or figures of this form have been given since 
those published by Leidy, the following descriptions and figures may 
be of interest, in that the young female is also described and figured 
for the first time: 
“¢Trayv. du Labor. de Wimereux, V, 1887, p. 70, and VIII, 1900, p. 226. 
PROCEEDINGS U.S. NATIONAL MUSEUM, VOL. XXXIV—No. 1593. 
