. 2 ECHINOIDEA. II. 



it may be very long, up to 3 ,nm (in a specimen from the Cape, German South Polar Expedition, it 

 reaches a length of 5 mra ). These pedieellariae are found almost exclusively on the abactinal side. 



The tridentate pedieellariae, which occur mainly on the actinal side, are of two kinds; one of 

 them is rather slender, the head reaching scarcely a size of o-5 mm . (PI. IX. Figs. 33—34, 36, 38). The 

 valves join in their outer half; the lower part is narrowed, sometimes even for some distance forming 

 a closed tube. There is, however, in this respect great variation; sometimes the valves join over 

 almost their whole length. The edge is distinctly serrate, and there may be a rather long tooth at 

 the point (in the Cape specimens, only slightly developed in the specimens from the Ingolf ). The 

 neck is well developed, the stalk compact. The other somewhat larger and coarser form (PI. IX. Figs. 

 15 — 16, 32) which mainly occurs on the actinal side and at the periproct has the basal part very 

 strongly developed, much larger than the blade; generally there is only a very slight narrowing be- 

 tween the basal part and the blade, sometimes, however, there is a rather deep sinuation. The edge 

 of the blade is very thick, finely serrate. There is a slightly developed neck, and the stalk is a little 

 widened at the upper end. This form, especially those with a deeper sinuation between the blade and 

 the basal part, reminds one very much of the short tridentate pedieellariae of Spafai/gas etc. That they 

 are really tridentate pedieellarite is evident from Cystechinus clypeatus, in which species all transitional 

 forms between such short coarse forms and the more slender forms are found. The triphyllous pedi- 

 cellarise have the blade a little elongate, finely serrate along the whole edge. (PI. IX. Fig. 26). They 

 are not distinctly different from small tridentate pedieellariae, in which the valves are hardly narrowed 

 in the lower part of the blade. 



The ophicephalous pedieellariae are generally exceedingly numerous, sometimes literally covering 

 the test on the abactinal side. They are of the typical spatangoid form (PL IX. Fig. 18, 37); there is 

 no neck, the lowermost and largest arc resting directly on the cup-shaped upper end of the stalk. 

 The blade has a rounded deepening, the edges are thick, widened somewhat wingshaped, finely ser- 

 rate down to the apophysis, where they join. The basal part is narrower than the blade. The lower- 

 most arc has a small prolongation at the point. The edge of the cup on the upper end of the stalk 

 is simple, not deeply sinuate as in the figure in the Challenger -Echinoidea. — The sphaeridiae are 

 rather elongate, more or less spinous; they may proceed to the 4th ambulacral plate in the bivium. 



Of the internal anatomy the figures 6, 8, 13 and 15, PI. VII give some information. There is a 

 well developed diverticulum and two siphones intestinales, the second, shorter one not separated from 

 the intestine. (In the Challenger -Echinoidea PL XXIX. b. 8 is figured the intestine of Cystechinus 

 Wyvillii, but neither diverticulum nor siphones are seen there. This would, indeed, be so very sur- 

 prising a difference between so nearly related forms that it may be allowed to suppose that a closer 

 examination will show these structures to occur also in Cystech. Wyvillii, and probably in all the Ur- 

 echinidas). - The stone canal is directed backwards on its way to the abactinal side, then passing a 

 rather long way forwards along the abactinal side to the madreporic plate. The axial organ is very 

 inconspicuous. The genital organs are rather small; those in Fig. 6. PL VII are full of nearly ripe eggs 

 which are ca. o\4 mm in diameter. 



This species was taken by the Ingolf at the following stations: 



