ECHINOIDEA. I. jj^ 



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 20™™. 



Of the formation of the interanibnlacral piates the following very remarkable statement is found 

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

 defined and seem to be distinctly separated from the coronal piates, yet new interanibnlacral piates 

 are not added independently as in the ambnlacral system and in the interanibnlacral system of other 

 young Echinids wliere the genital ring reniains permanently closed. The new interanibnlacral piates 

 are found to be pushing out from the piates of the anal system 011 eacli side of the genital piates. 

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

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

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

 some of the Sea-urchins of the present dav with Starfishes and Ophiurans on the one side and Holo- 

 thnrians on the other, than had been snspected formerly>. — This statement is completeh' incorrect. 

 The interambulacral piates are formed in P//. placenta as in other Echinids, not by the anal piates. 

 The -genital ring:, at all events, is closed, until the animal has reached a size of 17'"™ in diameter, 

 and so far accordingly the interambulacral piates must necessarily be formed in the comnion way, as 

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

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

 interambulacral piates, otherwise quite unknown among the Echinids, sliould then suddenly occur, is 

 very improbable — and, above all, x\gassiz has not at all proved it; all tliat niay be seen in the 

 larger specimens, is tliat the small anal piates directly adjoin the uppermost interambulacral piates. 

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

 of the present day , wliicli 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. København 1902 by the 

 nanie of Echinochcres globosus. 



Aræosoiiia fcnrstratiini. In a well preserved specimen from Blake > 1880 (with no more precise 

 locality) found in the museum of Paris, I have found the tetradactvlous iDedicellariæ together with as 

 well the large as the small form of trideiitate pedicellariæ. 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. fenestrahivi^ but are, no doubt, nevertheless to be interpreted as a 

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

 the interambulacral piates are lower in the middle, and widened in botli ends, in the former most of 

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

 — coinp. Bell (72)). The primary tubercles of the ambnlacral areas form on the actinal side a 

 rather regular longitudinal series out at the tube feet, in foirsfraf/iiii tliey are arranged more 

 irregularly. Otherwise 110 difference is found in the arrangement of the tubercles between this species 

 and /enestrafuin, oniy, perhaps, the secondary spines are somewhat more numerous in the new species. 



