100 
NOTES ON NORTHUMBRIAN TREMATODES. ! 
By M. V. LEJJOUK, B.Sc. 
Whilst investigating the mussel beds of Northumberland (i 
detailed account of which will be published hereafter) I found som 
interesting trematodes both in the mussels themselves and the othe 
Mollusca of the beds. A few notes on these may not be out of plac; 
here. 
An encysted trematode occurs in the foot of the mussel, Mytilu 
edulis, from Budle. This is the worm described by me from the foo 
of the cockle (Northumberland Fisheries Keport for 1004). It v?a> 
also later described more fully by Mr. Nicoll of St. Andrews (Ann 
and Mag. Nat. Hist., Jan. 190(3) from the foot of the mussel, cockle 
and Mactra stulturwn. I have also found it in the foot of My\ 
armaria and Maconia balthica. Mr. Nicoll has found what he be 
lieves to be the adult stage in the Oyster Catcher and the Herrin; 
Gull and he has given it the name of Echinostomutn secundum (Ann 
and Mag. Nat. Hist., June, 1906). The encysted stage is mor 
abundant in the mussel than in the cockle, nearly every specimen 
being infected. Besides the foot it is sometimes to be found in tin 
tissue forming the "floor" of the liver and, rarely, in the liver itseli 
In the cockle it occurs in the foot and in the mantle edge. It i 
easily seen from the outside m the cockle, showing as small tubercle 
all over the foot. In the mussel, however, nothing peculiar is visibl 
outside. I have found what I believe to be the previous' host o 
this worm in the common periwinkle Littorina littorea (see Plate I. 
Fig. I.) It occurred in one specimen of this mollusc out of twd 
examined in March, 1900, and m only one specimen out of 19t 
examined in June. The liver in these two periwinkles was full o 
the redia stage of a trematode and these redise were full of tailec 
cercariye of various sizes. The cercaria) agreed in many ways witl 
the encysted form in the foot of the mussel and cockle. The redia 
are a brilliant orange and the colourless transparent cercaria? shcn\ 
up against this bright background so that their shape is clearly seen 
The liver of the periwinkle is orange because it is packed full o. 
these redias, so it is easy to see whether the specimen is infected oi 
not. Each full-grown redia is about 1 mm. long, is of an elongateo 
