ECHINOIDEA. I. 



43 



found on the large pedicellarise; when this is the case, the spi- 



cules (fenestrated plates) will show that it is no Dorocidaris] 3. 



3. The large globiferous pedicellariae with large month; the blade not 

 prolonged. The stalk has no limb of projecting calcareous ridges. 

 The small pedicellarise without end-tooth. The spicules fenestrated 



plates Stercocidaris ingolfiana Mrtsn. 



The large globiferous pedicellarise with a little month at the 

 end of the somewhat prolonged blade. The stalk with a limb of 

 projecting calcareous ridges. The small globiferous pedicellarise 

 with end-tooth. The spicules spinous arcs Cidaris a/finis Phil. 



Fam. Echinothuridae. 



The classification of the Echinothnrids is distinguished by a pleasing simplicity; only three 

 recent genera are known, Phorniosoma^ Asthenosoma and Sperosoma, and, what is still more pleasing, 

 there are only two synonyms of these names, viz. Calveria W. Th., and Cyanosoma Sarasin. To the 

 genus Phorniosoma 10 species have been referred, to Asthenosoma u, and to Spcrosoma 2 species, most 

 of which species have been described by A. Agassi z, the rest by Wyv. Thomson, Koehler, Doder- 

 lein, and Yoshiwara, all during the last three decades. Here, then, we seem to have a division of 

 Echinids where the classification is in the best possible order. The joy, unfortunately! does not last 

 longer than until the moment when one has to determine Echinothurids oneself. Then one will soon 

 reecho the complaint of Sarasin: Wir wissen nicht, warum es A. Agassiz seinen Lesern so sehr 

 saner gemacht hat sich in seinen Challenger Echiniden zurecht zu finden. Um einen Echinothuriden 

 daraus zu bestimmen ist es notig die bei den einzelnen Arten gemachten Angaben sorgfaltig zu ana- 

 lysieren, unter Rubriken zu ordnen und dann die Bestimmung zu versuchen (352. p. 96). We might, 

 however, let that pass, if all the difficulties were to be superseded in this way; but this, unfortunately, 

 is not the case, as it will soon appear that the two large genera, Phorniosoma and Asthenosoma^ are 

 in reality not to be distinguished from each other with certainty. 



The chief difference between these genera is stated to be the fact that in Phorniosoma the 

 plates overlap each other in the whole length of the edge, while in Asthenosoma the plates are 

 narrower in the middle, so that naked interspaces are left only covered by the skin; only the broader 

 ends of the plates overlap each other in the way peculiar for the Echinothurids. Now there is, 

 however, the drawback by this statement that the arrangement of the plates is generally only to be 

 seen in dried specimens. But the Echinothurids are only very little adapted for preservation in dried 

 state, and if the material in hand be slight, one does not like to destroy it for the sake of determina- 

 tion. And even if the material is copious enough, so that it is possible to examine the plates exactly, 

 we are by no means sure to arrive at a result Bell (72) has shown that there is a considerable varia- 

 tion as to the size of the uncalcified membranous space between the plates: this may be quite conspi- 

 cuous or calcification may have gone so far, that it is difficult to detect the membranous interspace. - 



