ECHINOIDEA. II. 125 



single globiferoiis pedicellaria, resembling tliose of Scliizastcr Philippii, in a young specimen from llic 

 Mediterranean. 



The tridentate pedicellarioe occur, as has been said already, in two distinct forms, one with 

 elongate, slender valves, the otlier with short and robust \'alves. The slender form occurs in very 

 different sizes, from ca. ca'"™ to ca. a""" (length of liead). Tlie shape of tlic head is well seen in 

 Perrier's PI. VII. 4. a. The valves (PI. XVI. Fig.s. 1,9) are long and narrow, widely apart, joining only 

 at the point which is a little widened, spoonshaped, with the edges finely and closely serrate. The 

 edge of the lower, narrow part of the blade is more or less coarsely serrate, but it may sometimes be 

 quite smooth. The bottom of the blade is abruptly deepened in a narrow stripe along the median line, 

 with some crossbeams passing over it. In side view this dee])ening is seen as a narrow crest along 

 the back of the blade, in dorsal view of the blade it is seen as a sharply defined longitudinal keel, 

 formed by two knotted edges. The basal part is remarkably narrow; the apophysis is large, mostly with 

 smooth edge. The three points looking downwards from tlic basal part, mentioned and figured by 

 Perrier, I have never seen. 



In smaller specimens of this kind of pedicellarije the valves join to a larger extent, in quite 

 small ones they join in tlieir whole length. The blade is comparatively broad, simply leafshaped 

 (PI. XVI. Fig. 27). All transitional forms are found between the largest and the smallest specimen.s, as 

 is very well shown in the figures given by Doderlein. Two-valved specimens sometimes occur. 

 The neck is well developed, though rather short in the largest specimens. The stalk is an irregularly 

 fenestrated tube, with a small milled ring at the lower end for the attachment of the muscles, just 

 as in the spines, only, of course, much more feebly developed. Such a ring is found on the stalk of 

 all the pedicellarise except the ophicephalous ones. 



The second form of tridentate pedicellarise (PI. XVI. Fig. 8) is much coarser, witli a thick liead 

 and a short neck. The valves (PI. XVI. Figs. 7, 10) are much narrowed in the middle, but the ba.sal part 

 passes evenly into the blade (a rather conspicuous difference from J\Iacropnctis(cs spatangoidcs, (comp. 

 p. 128. PI. XVI. Figs. 3, 13). The edge of the outer part of the blade makes an obtuse angle with the 

 narrowed part; it is finely serrate. The point of the blade is generally somewhat produced inward.s. 

 There is a more or less developed meshwork in the lower part of the blade. The dorsal side of the 

 blade is uneven, knotted (PI. XVI. P^ig. 10). In larger specimens of this kind of pedicellarise the nar- 

 rowed median part of the blade may be rather long (PI. XVI. Fig. 25), such valves looking more like 

 usual tridentate pedicellaris. Perrier (Op. cit. p. 278)' names this kind ophicephalous pedicellarise in 

 spite of the fact that no bow is found below the valves. Now, to be sure, it may well be maintained 

 that it is no absolutelv necessary criterion for ophicephalous pedicellarise that these arcs must be 

 present (see also de Meijere. Siboga-Ech. p. 244— 45) — as well as, on the other hand, that sucli arcs 

 may occur also on undoubtedly tridentate pedicellarise, as has been shown both by de iMeijere and 

 bv nnself. In this case, however, it cannot be doubted that these pedicellarise are tridentate and not 

 ophicephalous, because true ophicephalous pedicellarise of quite typical structure are also found. — 



I At this place reference is made to a figure of a large tridentate pedicellaria (PI. VII. 4. ai, but tlie text and the 

 explanation of the plates leave no doubt that the Fig. 4. b is jueant, which eWdently represents a pedicellaria of this second 

 tridentate form. 



