Echinodermata, by Prof. F. J. Bell. 443 
secondary or smaller spines; in S. Raschi, on the other hand, 
this difference is, typically, hardly noticeable, and in corre- 
spondence with this the tuberculation is much more uniform. 
In one of the specimens of S. léaschi now lying before me the 
spines are as long and as prominent as in a specimen of S. 
purpureus of nearly the same size; in another, somewhat 
larger, the spines are much longer than we generally find 
them in S. Raschi; but they are much more uniform in size 
than in either the first-named specimen or than in S. purpu- 
reus, and, so far, the latter could not be confounded with the 
more common species. Nor could the first-named, but for a 
different reason; it is much higher than a S. purpureus of 
the same length, but the second specimen, though some 10 
millim. longer, is about 2 millim. less high, and, of course, 
looks much less high than its smaller companion. 
With the difference in the size of the spines there is, of 
course, correlated a difference in the size of the tubercles which 
bear them ; an inspection of Prof. Lovén’s figure* shows that 
the difference is not very marked in his type specimen. I 
removed the spines from a specimen which, in its spinulation, 
most closely resembles S. purpureus, and I find on cleaning 
the test that some of the tubercles are more than ordinarily 
larger than the rest; the general facies of this test is, however, 
distinctly that of S. Rascht. 
So, again, it may be noted that while some tests are less 
deep than others, others are more rounded; again, variations 
may be seen in the depth of the peristome. On the whole 
the most constant character of the deeper-water species appears 
to be the form of the labrum; this is always more pointed 
and convex than in S. purpureus. 
We may, then, observe with regard to a number of the so- 
called specific characters of S. Raschi that they vary within 
very wide limits. Of the specimens collected net one would 
be assigned to any other species, the general facies of S, 
Raschi being maintained throughout; but on analysis the 
several “ specific characters” are found for the most part to 
vary considerably. 
These observations seem to me to have some bearing on 
the question of the utility of specific characters, for they show 
that we must exercise the greatest caution in the selection of 
the points of structure which we use as such marks. It 
would be preposterous to imagine any zoologist more capable 
than Prof. Lovén of discriminating between two species of 
Echinoids, and yet among the characters by which his species 
* Ofy, Vet.-Akad. Férhandl. 1869, pl. xiii. 
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