20 NOMENCLATURE. 



all possible gradations from these mere catalogue names to short diag- 

 noses, short descriptions, or often a longer one, but not a whit more 

 useful. What is an ample description to a thorough student or a specialist 

 will fail most certainly to become adequate to the tyro or the master even 

 of a different department. Where shall we draw the limit? Shall we take 

 it for granted that our readers have the same material we have at their dis- 

 posal, which we know not to be the case, or shall we presume that the stu- 

 dent who is to consult the work has absolutely nothing except what any 

 given locality on the coast is likely to furnish him? What appears a most 

 simple question to be decided by a snap-judgment from small collections as- 

 sumes a totally different aspect when the materials have been drawn from 

 all possible quarters of the world ; and in a monograph like the present one, 

 to attach the same importance and to give an equal amount of space to 

 each species would be impossible, while a full description of the most char- 

 acteristic species of each genus (accompanied by figures) seemed the most 

 appropriate method of dealing with the subject, the descriptions of other 

 allied species becoming more or less comparative. 



At first sight the question of giving to each species its true name (that is. 

 the name it fust received) seems a perfectly plain one. the choosing of the 

 older being only a question of our ability to trace this; so it would lie were 

 we dealing with zoological equivalents. But what we now call our units 

 (our species) are not the units of the time of [innseus, or of the beginning 

 of this century, any more than our present units are likely t<> be those of 

 the last part of this century. Thus, at the very threshold of the question, 

 we introduce an arbitrary element in our appreciation (from our present 

 stand-point) of the condition of things at a different period. The names of 

 these collective species, as they have been called, certainly ought not to dis- 

 appear from the history of our science, if we can retain them by making 

 such a limitation of these old units as we find it possible to make with our 

 present units. Hence, when such a limitation has once been made for good 

 and sufficient reasons by a previous writer, no one ought, except for better 

 reasons, to attempt to make a revision of the limitation of these old names, 

 unless the material at his command, such as an examination of the originals 

 of the old author or carefully preserved tradition, evidently warrants him 

 in upsetting generally received combinations. In the interpretation of 

 such authors as Rumph, Breynius. Leske, Linne, when access to their collec- 

 tions is no longer possible (as their collections are irretrievably lost), we 



