I02 ECHINOIDEA. I. 



from the periproct. The buccal inembrane has inside of the buccal piates nniuerous small fenes- 

 trated piates imbedded in the skin; just ontside of the bnccal piates there are a few small piates, as 

 thick and complicate as the buccal piates, and like these set witli pedicellariæ. Nearest to tliese 

 piates some small, fine fenestrated piates are found, bnt all the rest of the bnccal merabrane is quite 

 naked. The globiferous pedicellariæ (PI. XIX. Fig. 20) are of the same form as in Ech. rlcgaus etc, 

 but only one tooth is found on either side. The tridentate pedicellariæ are more peculiar and of a 

 rather varying form (PI. XIX. Figs. 3, 33). The blade is broad and deep, without or with a quite feeble 

 net of meshes at the bottom ; the edge is more or less sinuate in the part where the valves join : 

 sometimes almost through the whole length (Fig. 3), soraetimes only in the outer half (Fig. 33); it is 

 finely serrate, but not thickened, and has no transverse series of teeth as in the £c/iimis-species men- 



tioned above. The «huge pedicellariæ covering the whole test , mentioned by Agassiz, are the 



globiferous pedicellariæ, which are rather long-stalked and conspicuous, not the tridentate ones. The 

 ophicephalous and triphyllous pedicellariæ of the common form; it nia\', however be noted that in the 

 latter the upper ends of the apophysis do not reach to the edge of the blade, and that there seems 

 to be a tending to a formation of a little mesh-work in the lilade. The stalks of the pedicellariæ of 

 the common structure; the spicules bihamate, very numerous. — That this species is not vmost closely 

 allied ; to £c//. jiorvcgicits, as Agassiz thinks (14. p. 11) is clearly shown by the characters here 

 mentioned. 



The description of Ech. iiinrgaritacciis given here agrees remarkably well with the description of 

 Stcrcchimis antarticus by Koehler (233. a.), and after having examined some specimens from v Belgica 

 which Prof. E. van Ben ed en has most kindly lent me, I must positively assert that it is Ech. ii/arga- 

 ritaceus\ no single character can be pointed out that might be a mark of distinction between them. — 

 Echinus diadema Studer is by Agassiz (Chall. Ech.), Bernard (79), and M eis sner (2S51 thought to 

 be synonymous with Ech. »largaritaccus. Studer (386) admits, to be sure, that the}' are very similar, 

 but thinks that some difference is found in the pedicellariæ — i. e. the ophicephalous ones. Now it 

 is true that his figures show a slight difference; but the ophicephalous pedicellariæ are generally of 

 very little importance with regard to the distinguishing between the species, and yield only quite 

 exceptionally good specific characters (as in Ech. aflai/ficus). In this case there can be no question of 

 distingiiishing between the two species;:, either by the ophicephalous or the other pedicellariæ. After 

 having examined some specimens, determined by Studer himself as Ech. diadema, which I have 

 received for examination from the museum at Berlin, I must decidedly follow the mentioned authors; 

 Ech. diadema cannot be distinguished from Ech. margariiaccus. 



Echinus horridus A. Ag. is not closely allied to Ech. iiorvegicus, as stated by Agassiz (Chall. 

 Ech. p. 116); its nearest relation is no doubt Ech. »largaritacais. The spines are quite as in this 

 species, and also the pedicellariæ are very similar to tliose of the latter species. The tridentate 

 pedicellariæ (PI. XIX. Fig. 2) are rather much open and rather sinuate in the outer part, where the 

 valves meet; they may become pretty large (a little more than i"""), and then they have a rather 

 strong, coarse net of meshes in the blade (it may be described as cross-beams rather far from the 

 bottom). In the globiferous pedicellariæ (PI. XIX. Fig. 22) cross-beams are wanting between the edges 

 of the blade (also in young Ech. margaritaceus they may be fovind without cross-beams), and there are 



