Bell — Echinoderms collected hy the 88. " Fingal." 62S 



wliicli a well-marked spine was present on nearly every plate, I 

 felt that it would be difficult to convince any one of their specific 

 identity, and that notwithstanding the fact that they came up 

 from the same spot and had the same characteristic wedge-shaped 

 infero-marginal. 



Fortunately, however, there were other specimens, and I found 

 that of the seven two had the supero-marginals quite spineless, twa 

 had a few spines, 2 mm. long, scattered irregularly on the plates 

 near the base of the arm ; in a fifth similar spines extended some 

 way along some hut not all of the arms ; the same was the case 

 with the sixth specimen, while in the seventh spines were 

 developed with considerable regularity at the bases of the arms, 

 and were replaced on the distal supero-marginals by spiniform 

 tubercles. 



The more one works at Echinoderms the more one sees how 

 species vary, but I do not think that a more unexpected example 

 than this has ever yet been put on record. 



It conveys two clear lessons — the first is that, when we think 

 we have got a " new species " we should examine with care an 

 extensive collection to see if we cannot link on our new form to 

 some known species whose variations we only imperfectly know ; ^ 

 the other is that in the description of a species we cannot be too 

 careful in eliminating what is individual, and be watchful to 

 remember that we have to define not a specimen but a species.^ It 

 is the habit of systematic zoologists to talk about describing a new 

 species ; it would be well to speak always of diagnosing it. De- 

 scription without diagnosis is nothing worth. 



The following appear to be the characteristics of this un- 



^ An instructive example of this has lately happened to myself. Professor Herdman 

 was good enough to send a specimen of an Echinoderm from Norway, which was re- 

 markable for having seven pairs of pores in an arc ; Strongylocentrohis drobachiensis is- 

 ordinarily said to have five or six pairs, and a survey of the extensive series in the 

 British Museum showed that this statement was quite correct. Satisfied, however, 

 that I had nothing but an example of the first-mentioned species before me, I continued 

 the moDotonous business of counting till I came on a specimen in which a plate bearing 

 eight pairs of pores was intercalated between two bearing six pairs ; the corresponding 

 plates in the other half of the ambulacrum bore seven each. 



2 The history of the spec;ies of Cijcethra is very instructive : cf. Perrier in Miss., 

 Sci. du Cap Horn, vi., Echinodermes (Paris, 1891), pp. 122-5 and 170-188. 



