ECHINOIDEA. I. 



radiary canal), is found from the earliest stages, and not, as stated by Agassiz (op. cit. p. 35), only 

 formed, when the animal has reached a size of 2O mm . 



Of the formation of the interambulacral plates the following very remarkable statement is found 

 in Agassiz (op. cit p. 32): On the abactinal system ... while the plates of the genital ring are well 

 defined and seem to be distinctly separated from the coronal plates, yet new interambulacral plates 

 are not added independently as in the ambulacral system and in the interambulacral system of other 

 young Echinids where the genital ring remains permanently closed. The new interambulacral plates 

 are found to be pushing out from the plates of the anal system on each side of the genital plates. 

 As the ocular and genital plates of the genital ring become separated with increasing size, the addi- 

 tional anal plates formed in the intervening spaces are pushed out, and become a part of the abactinal 

 portion of the interambulacral area. . . . This shows a far closer relationship between the young of 

 some of the Sea-tirchins of the present da}' with Starfishes and Ophiurans on the one side and Holo- 

 thurians on the other, than had been suspected formerly*. - - This statement is completely incorrect 

 The interambulacral plates are formed in Ph. placenta as in other Echinids, not by the anal plates. 

 The genital ring, at all events, is closed, until the animal has reached a size of ly 1 " in diameter, 

 and so far accordingly the interambulacral plates must necessarily be formed in the common way, as 

 may also easily be substantiated. In a specimen of a diameter of 30""" a couple of ocular and genital 

 plates are still joining, and here the case is quite the same. That a new mode of formation of the 

 interambulacral plates, otherwise quite unknown among the Echinids, should then suddenly occur, is 

 very improbable -- and, above all, Agassiz has not at all proved it; all that may be seen in the 

 larger specimens, is that the small anal plates directly adjoin the uppermost interambulacral plates. 

 Thus the more close relation between Asterids, Ophiurids, Holothurids, and some of the Sea-urchins 

 of the present day, which Agassiz derived from this feature, is quite illusory. 



Calveria gracilis. - - The parasitic Copepod from the spines of this species, mentioned on p. 51, 

 has been described by Dr. H. J. Hansen in Vidensk. Medd. fra Naturh. Foren. Kobenhavn 1902 by the 

 name of Echinochcres globosus. 



Araosoma fenestratum. In a well preserved specimen from Blake> 1880 (with no more precise 

 locality) found in the museum of Paris, I have found the tetradactylous pedicellariae together with as 

 well the large as the small form of tridentate pedicellariae. If still some doubt might be left of the 

 correctness of my interpretation of this species, no doubt will hereafter be possible. 



Through Prof. Bell I have from Department in the course of fishing investigations* received 

 some specimens of an Echinothurid from west of Ireland (Porcupine Bank, 199 fathoms) which 

 prove to be closely allied to A. fenestratum, but are, no doubt, nevertheless to be interpreted as a 

 separate species. The structure of the test differs somewhat from that of A. fenestrattim. In the latter 

 the interambulacral plates are lower in the middle, and widened in both ends, in the former most of 

 the plates are not widened at all in the outer end. (This character, however, is scarcely very reliable 

 comp. Bell (72)). The primary tubercles of the ambulacral areas form on the actinal side a 

 rather regular longitudinal series out at the tube feet, in fenestrahim they are arranged more 

 irregularly. Otherwise no difference is found in the arrangement of the tubercles between this species 

 and fenestratum, only, perhaps, the secondary spines are somewhat more numerous in the new species. 



