44 TH. MORTENSEN, (Schwed. Sudpolar-Exp. 



plus gros sur les ambulacraires; dix rangs, dont le median de chaque cote plus gros 

 sur les anambulacraires; les series des plus gros tubercules convergentes vers l'ouver- 

 ture inferieure; epines et auricules: Couleur de chair avec les tubercules verts. » 



»Cette espece qui existe dans la collection du Museum vient peut-etre des mers 

 australes, suivant M. de Lamarck. » 



It is perfectly clear from this description that this species cannot be identical 

 with the margaritaceus of Agassiz; the tuberculation is decidedly different, as is 

 also the colour. And the last remark proves beyond doubt that BLAINVILLE has 

 seen the type specimen, from which he evidently has made the description. In fact 

 this description much more recalls a form like Sphcerechinus granularis. The fact 

 that the species is placed in the genus Heliocidaris in AGASSIZ & DESOR's Cata- 

 logue raisonne» is also very much against A. Agassiz' interpretation of the species. 

 The type specimen having been lost, it is impossible now to determine with cer- 

 tainty which species Lamarck's Echinus margaritacais was; it can only be said 

 with certainty that it was not the species which A. AGASSIZ described under that 

 name. The figures given by VALENCIENNES in the Atlas of the »Venus« do not 

 help us to more certainty, the specimen having likewise been lost*; but they like- 

 wise show with certainty that it is not the species called margaritaceus by AGASSIZ ; 

 especially the fact that there is a primary tubercle on every ambulacral plate is im- 

 portant, the species called margaritaceus by AGASSIZ having a primary tubercle 

 only on every second or third ambulacral plate. DODERLEIN (Op. cit. p. 218) does 

 not think it right to trust the correctness of VALENCIENNES' figures in such details: 

 »Ich glaube nicht, dass man aus der sehr schematischen Figur von Valenciennes mit 

 Sicherheit einen Schluss ziehen darf, ob im Ambulacralfeld jede einzelne oder jede 

 zweite Platte eine Primarwarze trug; mit dieser Annahme hat wohl Mortensen die 

 Genauigkeit der farbigen Figur iiberschatzt.» I must object to this that it is not the 

 coloured figure from which I conclude that VALENCIENNES' Ecli. margaritaceus has 

 a primary tubercle on all the ambulacral plates, but from the detail-figures i.b. and 

 1. c, which are not at all schematic, but evidently as exact and careful as any of 

 the best figures of details of the test structure of Echini since published. In the 

 detail figures of ^Echinus pileolus-* (PI. 9) it is very exactly shown that only every 

 second ambulacral plate has a primary tubercle; there is then no reason to suppose 

 that in the case of Echinus margaritaceus the figure should be so very incorrect, as 

 it would be if it represented the species called margaritaceus by AGASSIZ. 



In short: we cannot any longer with certainty unravel which species was really 

 meant with Lamarck's Echinus margaritaceus; but it is certain, from the descriptions 



* Even if this specimen were preserved, it would still be very questionable, whether it was really 

 identical with Lamarck's Ech. margaritaceus ; the tuberculation is not at all in accordance with Lamarck's 

 species, as described especially by Blainville. 



