A discussion of certain questions of nomenclature, as applied to parasites. 177 



must be taken as a comfort, and when we are inclined to blame 

 fortune that the irritating changes involved fall to a great extent to 

 our generatioD, we can comfort ourselves with the thought that our 

 inconveniences — exasperating as they often are (few helmiothologists 

 appreciate this more keenly than I do, dealing daily, as I do, with a 

 Card catalogue of at least 300 000 entries !), will aid future generations 

 in more easily dealing with the increased number of genera and 

 species which will fall to their lot. And when we feel as if we wished 

 to rebel against that "fetich", the lex priori tatis — as we all 

 occasionally do feel — let us not forget that our generation is not 

 the only one to which zoology and a stable System of zoological names 

 are of interest. We should, on the other band, recall that to refuse 

 to undergo the inconveniences, to which we are occasionally submitted, 

 is to confess a lack of altruism which unfits a man for the scientific 

 professions. 



9. UnaTailaWe, available, and yalid names. 



Any genus or species may have an unlimited number of available 

 and unavailable names, but it can have only one valid name at a 

 given time ; while the valid name may under given circumstances be- 

 come unavailable and hence invalid. It is essential that we should 

 have a clear idea of the three classes of names and should use only 

 the valid name, where this is clear; for the careless use of an un- 

 available or an available (yet not valid) name of one species may 

 frequently necessitate the rejection of the name which is valid for 

 another form. These names may best be understood, if we take an 

 example, first of a generic name, then of a specific name. Given the 

 following table of synonymy: 



1808. Hemiurus E,ud. (type: apiiendiculatus) [nee Hemiurus 1855; nee 

 Hemiura Ridgwat, 1887]. Present valid name by lex priori- 



tatis. 



1809. Distoma (Apohlema) Duj. Distoma (type : hepaticum) is unavail- 

 able in this genus because hepaticum is not congeneric with 

 appendiculatus, but is congeneric with Fasciola, 1758, which 

 antedates it. Apohlema (type: appendiculata) is available at 

 any time, and if Hemiurus^ 1808, should be shown to be un- 

 available by the rule of homonyms, Apohlema would become 

 valid. - 



1886. Eurycoelum Brock (type: sluiteri) is unavailable according to 

 Blanchard, Jentink, and others, because of Eurycoelus, 1848; 

 it is available according to Jordan, Evermann, Stilbs, and others, 



