416 WILLIAM NICOL. 
related, but in my opinion D. laureatum does not belong to 
the genus of which D. metccus is the type. The widely 
different hosts might in the first place raise doubt as to the 
close relationship of the two forms, although, as Braun 
remarks, too great weight need not be attached to this, 
because the larval stages of both may be passed through in 
insect larvee forming food common to bats and fishes. We 
may therefore neglect this. 
The close resemblance between the two species, however, 
is not borne out on more detailed examination. Several 
important features of difference are apparent. ‘The first, and 
possibly the chief of these, is the condition of the circum-oral 
swelling and papille. Braun did not fail to notice the 
difference here, but he under-estimated its importance. In 
Crepidostomum metcecus the circum-oral collar is confined 
almost entirely to the dorsal surface of the sucker. It does 
not extend on to the ventral surface, and thus its edges are 
at some distance from the aperture of the sucker. In Dist. 
laureatum the collar completely encircles the sucker and its 
edges are contiguous with, or even project into, the aperture. 
There are thus no ventral papille in C. metcecus, all bemg 
dorsal, or at most two being dorso-lateral. Further, they are 
only five in number as opposed to six in D. laureatum. 
Braun’s attempt to correlate the discrepancy is certainly 
ingenious, and possibly explains to some extent the origin of 
the papille and the increase in their number. He considers 
that the median dorsal papilla in C. metcecus which is 
furcate (zweizipfehg), must be regarded as a double papilla, 
and as such is equivalent to the two dorsal papille of D. 
laureatum. The division of this median papilla would 
certainly make the number six, but unfortunately Braun 
ignores the tact that (from his own description, p. 230) the 
two neighbouring papille are not altogether simple, but 
appear to approach the middie papilla in shape, 1. e. to be 
two-pointed or bi-partite. These have equal claim to be 
regarded as ‘ Doppelpapillen,” and in this way the number 
would be eight. There is no evidence of such splitting of 
