«L,oiii d'étre nuisible aux vrais progrés de la science, 

 cette multiplication des genres, lorsqu'ils sont établis sur 

 des caractéres précis, ne saurait avoir d'autre effet que de 

 rapprocher de plus en plus les espéces, que leurs caractéres 

 naturels Hent le plus étroitenient. C'est lå le grand avantage 

 des petits genres, et eet avantage est surtout sensible dans 

 les families, dont toutes les espéces se ressemblent par leur 

 aspect extérieur et par 1' ensemble de leurs caractéres. . 



L. Agassis. 



On generic and specific Characters in the Echinoids. 



Everybody who has studied Echinoids, will have felt a considerable difficulty in recognising many 

 of the genera, at all events of the regular Echinoids. Snch was, at any rate, my case at the commen- 

 cement of my researches. I studied the excellent collection of these animals found in our museum, 

 and found it to be more and more hopeless. A great many genera were exhibited, as: Echinus, 

 Psammechinus, Toxopncusfcs, Hipponoe^ Bolciia, Psilcchimts^ Lytcchimis^ Loxechhms, etc; but it seemed 

 to be impossible to discover the characters on which they were established, whether the naked tests, 

 or specimens that had kept the spines, were examined. And the literature did not contribute very 

 much to clear up the question. To be sure, some of these names ( — as it will be seen, partly 

 unjustly — ) appeared to be synonyms; but nevertheless the other genera were not much better 

 characterized. We learned through long descriptions that the spines were thick or thin, few and scat- 

 tered, or many and closely packed; that the tubercles might be small or large, and that they might 

 be placed in more or less regular series, etc. — altogether things easily enough seen, but so relative, 

 that it was impossible to get any any firm hold. It was almost enough to drive one to despair. 



Still a faint hope was left. Might not the difficulty be in the literature, and the animals them- 

 selves in reality be less intractable? A profound and careful attempt at penetrating into the mysteries 

 of the relationship of the Echinoids was plauned, and the plan was the simple, but clear one: to let 

 literature alone for the present, while the animals were studied thoroughly. Everything had to be 

 examined that might in any way be supposed to show systematic characters: the test, the spines, 

 the tube-feet, the pedicellariæ, the spicules, the sphæridiæ, etc. The beginning was to be made 

 with the Ecåimis-species. This choice seemed to be the best one, as these sjjecies have hitherto been 

 especially notorious for their difficulty, and a very rich material of them is found in the museum of 

 Copenhagen. The result was excellent. The animals proved to be very tractable, the species to be 

 very well characterized (with a few exceptions). The difficulties arise from the literature containing 

 numberless bad descriptions. And what a confusion is reigning in the literature with regard to 

 the names. Almost every species must drag along with it a lot of synonyms, not only specific syno- 

 nyms, but also generic ones. Several species have by and by been referred to a whole series of different 

 genera, to end at last as a separate genus, as badly characterized as most of the other genera. To 

 name only one instance: The genuine Psa///mrc//i>/Hs-species: varicgatus (Lamk.) and scmittiberculatus 

 (Val.) have by and by been referred to the following genera: Echinus^ Lytec/mius, Schizechinus^ Toxo- 

 pnetisics, but only rarely, in recent times not at all, to the genus to which they decidedly belong. 

 On the other hånd the following extraneous species have been referred to Psammechinus: Ecliinus 

 norvegicus, magcllanicus^ miliaris, microtubcrculatus^ angiilosus^ Strongyloccntrotus Gaimardi, iniermcdius, 



