Vi INTRODUCTION. 
may serve as the northernmost boundary of our area, is responsible 
for a considerable proportion of the increase ; but, so long as the 
species belong to groups which are not essentially abyssal forms, it 
is better to include than exclude them from a work which differs 
widely from that of Forbes in that it is published at a time when 
dredging at considerable depths is becoming a pastime as well as a 
serious business. 
In the preparation of the diagnoses I hope I shall not be thought 
to have erred on the side of brevity ; if I have been brief, I have 
done my best to avoid being obscure. Where a writer fills page 
after page with description he will indubitably fail if his object be to 
make himself intelligible to others. My first object has been to 
make every point clear, and I have not stinted myself in the use of 
keys, artificial or otherwise, which would show what I meant. 
If in the portion of this work which deals with the Asteroidea I have 
_ in any way failed to give an accurate account of Mr. Sladen’s opinions 
or diagnoses,,I must ask to be accounted innocent. I have devoted 
many hours to his Report on the Starfishes of the ‘ Challenger,’ but 
in consequence of the minuteness of his descriptions of species, the 
frequent absence of any indication of the diagnostic characters of 
his genera, and the repeated expression of views for which he does not 
give (I do not say does not possess) adequate reasons, they have not 
been as fruitful as I could have wished. That the number of species 
and genera which Mr. Sladen has created will be largely reduced I 
am convinced, and I feel confident that the majority of naturalists 
who devote themselves to the study of Starfishes will agree that the 
species vary greatly. I cannot say how deeply I regret the extreme 
divergence that exists between Mr. Sladen’s views a well as methods 
and my own. But I cannot assent to or approve of a mode of study 
which practically results in the description of specimens instead of * 
the diagnosis of species, and I note with satisfaction that the 
accomplished student of Echinoderms at the Jardin des Plantes 
ranges himself on the same side as myself. 
To me, indeed, and, I believe, to many others, one of the reasons 
why the study of Echinoderms is so fascinating is that they present 
so many and such striking variations ; these very variations are, of 
course, the cause of the difficulty of the study, in which there is a 
