W. Nicoll 
343 
most observers have not troubled to deal with such matters. A detailed 
statistical account would, however, be of interest. 
Some note must be made on the subject of classification. Odhner 
(1911) has done more than any other recent writer to help in arranging 
the various groups of parasites in systematic order. Although his 
opinions are difficult to agree with in certain cases yet his system is 
followed in this paper as it is the most rational which has hitherto 
been offered. He has to a certain extent outdone Looss in his pre¬ 
cision of detail, e.g. in his subdivision of the Fellodistominae, but 
on the other hand he has shown a welcome tendency to a broad inclusive 
view of taxonomy in his treatment of the HEMIUR.IDAE. As in other 
branches of zoology, the dividing line between species and genera is 
difficult to fix. The simplicity and naturalness of Looss’s system were 
obvious and the system was at once almost universally accepted. Odhner, 
however, has discovered details, chiefly in regard to the excretory system 
and the terminal male genitalia, which he considers of extreme systematic 
importance and which are not by any means obvious on casual observa¬ 
tion. With regard to the male genitalia, Odhner’s vieAvs are undoubtedly 
sound, but it remains to be proved whether his ideas regarding the form 
of the excretory system are based on a firm foundation. 
The references, given are, as far as possible, those likely to be most 
readily accessible to English workers. In a large number of cases, 
however, only reference could be made to works which are exceedingly 
difficult to obtain. This applies chiefly to the work of older writers, 
but a number of extremely important modern monographs, e.g. Looss 
(1894) and Odhner (1905), are not by any means easy of access. 
LIST OF THE TREMATODE PARASITES FOUND IN BRITISH 
Marine Fishes, arranged systematically. 
Order DIGENEA. 
Sub-Order PROSOSTOMATA. 
Super-Family DISTOMATA. 
Family Allocreadudae 
Sub-Family Allocreadiinae 
Authority. 
Genus Podocotyle 
1. P. atomon (Rud.) 
2. P. reflexa (Crept) 
3. P. syngnathi MooU 
4. (P.)/wrcata Bremser 
5. (P.) atherinae Nicoll 
Odhner 1905, Lebour 1908. 
Dujardin 1845, Monticelli 1893. 
Nicoll 1914. 
Odhner 1905. 
NicoU 1913 a. 
