342 
Trematodes of Marine Fishes 
{Pleuronectes platessa). The latter fish, hke the whiting, is one of those 
which have been most systematically examined. 
Of the fishes in which the British records are exceptionally defective 
the outstanding examples are the sun-fish {Mola), the common eel and 
the sturgeon {Acipenser sturio). The first of these, as already noted, 
is exceedingly rare in British waters, while the other two can hardly 
be regarded as marine fishes in the true sense of the term. 
Of the essentially British marine fishes in which there are obvious 
gaps in our records, the chief are the angler {Lophius), the bull-head 
{Coitus scorpius), the turbot {Botlius maximus), the smelt {Osmerus 
eperlanus) and the rockling {Onos tricirratus). In the case of the first- 
mentioned the records in many instances probably represent adventitious 
parasites. In the case of the bull-head the list is swelled by a number 
of apparently purely Arctic forms. With regard to the turbot, three 
at least of the records are extremely doubtful. The rockhng displays 
a number of doubtful records, while the smelt shows three which require 
revision. 
With regard to the fishes which may be most rehed on to furnish 
Trematode parasites, an important matter for demonstration purposes, 
the whiting, as previously mentioned, stands preeminent. It is, 
unfortunately, a fish which undergoes very rapid decomposition and 
on that account it is perhaps less reliable than the cod and the pollack 
for providing living parasites. Next to the whiting the grey gurnard 
is undoubtedly the most productive of British fishes in the matter of 
Trematode parasites. The red gurnard {Trigla pini vel cuculus), 
where it can be obtained, is almost as good. The common dab 
[Pleuronectes limancla) is perhaps as reliable a host as any and its 
ubiquitous distribution renders it easily obtainable in most locahties. 
Failing it the plaice (P. platessa) and the long rough dab {Drepanopsetta 
platessoides) are almost equally suitable. Next to these commoner 
fishes come the less common spotted wrasse [Labrus berggylta) and the 
angler [Lophius piscatorius), both of which are fertile sources of Trema¬ 
tode parasites in the localities in which they occur. Mention must 
also be made of the horse-mackerel and the conger-eel, both of which 
are constantly infected though not by such a great variety of parasites 
as the previously-mentioned fishes. 
Some indication of the frequency and the number of the parasites 
in their various hosts might have been desirable. I have attempted 
this in a previous paper (1909 b), but in the present instance such 
records would be misleading and valueless on account of the fact that 
