124 Trans. Acad. Set. of St. Louis. 



held by Try on, it would seem more natural to regard these 

 genera only as the representatives of subfamilies — Pleuro- 

 tominae and Haliinae — which alone would compose the 

 Pleurotomidae. It is possible, however, if not highly 

 probable, that some of the originial subgenera of Tryon, such as 

 Donovania (Lachesis) and MitromorjjJia, may really rank 

 as subfamilies or even belong to widely different families. 



Probably the course coming nearest to the truth of the 

 matter would be to treat the Pleurotomidae in accordance 

 with the common practice in equally extensive and complex 

 families of arthropods and other classes of animal life, — that 

 is to divide the family or subfamily into tribal sections, each 

 of which is to be separated into more or less definitely limited 

 groups of species which may be known as genera and com- 

 prising also, in some special cases, other minor groups or sub- 

 genera. The alternative course and the one usually followed 

 in the literature of the Mollusca, would be to divide the 

 families or subfamilies into a comparatively small number of 

 genera, to which a relatively very large number of minor 

 groups are to be attached as subgenera. In the latter case I 

 find it impossible to scientifically define these supergenera, and 

 another objection to this alternative method is that it gives 

 rise to too cumbrous a nomenclature. In the present state of 

 ignorance of true relationships and exact taxonomic weights 

 or values, a name once printed and introduced to nomenclature 

 may as well be regarded as the true surname of the species 

 as of subordinate value, for a subspecies under the latter con- 

 dition must be represented by four words, and, instead of 

 adhering to the binomial system, we would be shaping a 

 course strongly suggestive of a reversion to the pre-Linnean 

 custom of descriptive names or short descriptive diagnoses 

 and the manifest advantages of the binomial system would be 

 thrown away. It is impossible to devise a system of nomen- 

 clature which will serve to indicate at a glance, by the 

 form of the names, exactly the weight or value of taxonomic 

 relationship or isolation and it may as well not be attempted. 

 When we print a tabular statement of species or genera based 

 upon structural characters, we do not by any means desire it 



