11 



dark impressions may sometimes dhough seldom) be in- 

 distinct. Tlie number of tubercles on the apical plates is 

 very variable, there may even be none at all. The form 

 of the apical plates is also rather inconstant. In the figure 

 the madreporic plate is seen to spread over the adjoining 

 ocular plates and also over another small plate. The diameter 

 of the apical system is distinctly larger in this species than 

 in the other ones. (Comp, the measures given below). 



The pedicellariæ. Perkier in his well known work 

 on the pedicellariæ has given a good figure (PI. 4. la) of 

 the head of a smaller tridentate pedicellaria, the only one ^i^'f'^;, sIZme!'S^jL). 

 he has found ; he names the species I), savignyi, but it 



must certainly be the true D. saxatile. (That the D. turcarum of Perkier is 

 synonymous with D. saxatile (setosum), as stated by Agassiz (Rev. of Ech. p. 104) 

 and Foe:ttingek '), I must doubt on account of the pedicellaria figured by Perriek 

 (Pl. IV. 2) being much broader than those of D. saxatile). A second form of pedicel- 

 lariæ has been described and figured by Foettinger (Op. cit. p. 485. P1.28. u.); it is 

 named „claviform" pedicellaria. The same form has been described and figured 

 by DE Meijere (Op. cit. p. 50. Taf. XIV. Fig. 203). This is, I believe, all that is 

 known of the pedicellariæ of this species, those figured by Agassiz (Rev. of Ech. 

 PI. XXIV. Fig. 38) evidently not belonging to D. saxatile, but, probably, to D. antil- 

 larum ; his Fig. 89 is so little characteristic that it may be said to represent a very 

 small tridentate pedicellaria of any of the Diadema-s])ecies. 



Three kinds of pedicellariæ are found, viz. tridentate, triphyllous and ophi- 

 cephalous (claviform) ones. The tridentate pedicellariæ occur in two forms, a large 

 and a small one, which are, however, not sharply distinguished. In the large form 

 (PI. III. Fig. 22, 29. PI. V. Fig. 2) - length of head upto 2 mm. — the valves are narrow, 

 straight and wide apart, joining only at the point. The blade is rather deep, with a 

 well developed smooth mesliwork at the bottom reaching about the middle of the blade 

 or even farther out. The edge is coarsely dentate in the whole length, only at the 

 point the serrations are finer; in the lowermost part of the blade the edge with 

 the dentations is mostly bent a little outwards. The neck of this kind of pedicel- 

 lariæ is very short. In the smaller form of tridentate pedicellaria' (PI. III. Fig. 23. 

 PI. V. Fig. 5, 8) — length of head c. 0,1 —-2 mm. ~ the valves are a little curved; they 

 are wide apart, joining only at the point. The blade is essentially of the same loini 

 as in the large tridentate pedicellariæ, but there is no meshwork at the bottom and 

 the edge is quite smooth or with a few dentations in the lower part. The point 

 is a little widened, forming a distinct angle with the side-edge of the blade. The 



')Sur la structure des Pédicellaires gemmifornies de Sphærechinus granularis et d'autres Echinides. 

 Arch.de Biol. 11. 1881, p. 485. 



2' 



