102 ECHINOIDEA. I. 



from the periproct The buccal membrane has inside of the buccal plates numerous small fenes- 

 trated plates imbedded in the skin; just outside of the buccal plates there are a few small plates, as 

 thick and complicate as the buccal plates, and like these set with pedicellarise. Nearest to these 

 plates some small, fine fenestrated plates are found, but all the rest of the buccal membrane is quite 

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

 but only one tooth is found on either side. The tridentate pedicellarise 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), sometimes only in the outer half (Fig. 33); it is 

 finely serrate, but not thickened, and has no transverse series of teeth as in the cfo'mis-species men- 

 tioned above. The huge pedicellarise covering the whole test, mentioned by A gas si z, are the 



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

 ophicephalous and triphyllous pedicellarise of the common form; it may, 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 blade. The stalks of the pedicellariae of 

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

 allied to Ech. norvcgicus, as Agassiz thinks (14. p. n) is clearly shown by the characters here 

 mentioned. 



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

 Sterechinus antarticus by Koehler (233.3.), and after having examined some specimens from Belgica 

 which Prof. E. van Beneden has most kindly lent me, I must positively assert that it is Ech. marga- 

 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 Meissner (285) thought to 

 be synonymous with Ech. margaritaceus. Studer (386) admits, to be sure, that they are very similar, 

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

 is true that his figures show a slight difference; but the ophicephalous pedicellariae 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. atlanticus}. In this case there can be no question of 

 distinguishing between the two species, either by the ophicephalous or the other pedicellariae. 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. margaritaceus. 



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

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

 species, and also the pedicellarise are very similar to those of the latter species. The tridentate 

 pedicellariae (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 ram ), 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 pedicellariae (PL XIX. Fig. 22) cross-beams are wanting between the edges 

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



