56 



ECHINOIDEA. II. 



showing some tendency to dissolution in this group. To determine with certainty which of the other 

 plates in the apical area of this species ought to be regarded as basal or as «intercalated plates is 

 scarcely possible, and I cannot feel convinced either that the interpretation of these plates in P. ductus 

 given by A gas si z is quite correct. — The genital openings are present in a specimen of i3 !nm , but 

 have not yet appeared in a specimen of n mm . 



The primary tubercles are scattered quite without order over the whole test, except the ambu- 

 lacral plates joining the sternum and episternum. A great number of small tubercles are found among 

 the primary ones. On the primary interambulacral plates, which are all in contact with the peristome, 

 the tubercles mav be rather numerous, forming- like a rudimentarv bourrelet. The larger ones of the 

 plates of the peristome may carry a single tubercle (spine). — The primary spines (PI. X. Figs. 21,31) are 

 ca. 3 mm long, slender, gracefully curved, more or less spinous, a little widened towards the point. The 

 spines of the sternum are rather widened in the point and hollowed (PI. X. Fig. 38). The spines round 

 the actinostome are not distinctly clubshaped. The miliary spines (PI. X. Fig. 32) are short, ca. o - 5 mm ; 

 the point is widened and serrate, more or less flattened. The clavula; of the fasciole do not differ from 

 the other miliary spines. 



The tubefeet of the two or three inner ambulacral plates are penicillate, forming a rather con- 

 spicuous phyllode. The rods supporting the filaments of these tubefeet are irregularly fenestrate, rather 

 coarse (PI. X. Fig. 37); the spicules (PI. X. Fig. 27) are arranged in two series; they are of the same general 

 shape as in Urechintis. The tubefeet of the anterior ambulacrum are rather large, but simple; a more 

 or less distinct calcareous ring, formed by some few irregular, fenestrate plates is found, at the point 

 of the simple tubefeet. — The sphaeridiae are found only on the inner one or two pairs of ambulacral 

 plates, generally only one on each plate. They are rather elongate, smooth (PL X. Fig. 25). 



The pedicellariae are represented by the four usual forms. The globiferous pedicellariae (PI. X 

 Figs. 23, 34) are very peculiar; the blade forms a short but rather wide tube, which ends with a large 

 round opening, sometimes prolonged a little downwards on the inside; the edge of the opening is 

 rather finely serrate, except on the lower side. No neck; the stalk is rather thick. --It may, indeed, 

 be regarded as a little doubtful whether this form really represents the globiferous pedicellariae, since 

 there is no thick skin covering the valves, as is the case in the related genera Urechinus etc. But 

 on the other hand it is rather similar in structure to the undoubted globiferous pedicellariae of Ure- 

 chinus giganteus, Wyvillii etc., and it would be more unnatural to refer it to any of the other kinds 

 of pedicellariae. (The glandular tissue mav perhaps be found within the tubeshaped blade). The triden- 

 tate pedicellariae (PI. X. Figs. 2, 16, 36) are small, the largest ones only ca. o'3 mm . The blade is simply 

 leafshaped, sometimes shorter and almost round; the edge is serrate, generally with some longer 

 teeth at the point. The figure 15. PI. X represents a somewhat different form, with the blade more 

 narrow and the apophysis ending down in the blade. I have not seen transitional forms between the 

 two kinds of tridentate pedicellariae. The ophicephalous pedicellariae (PL X. Fig. 19) are very simple, of 

 the usual structure; the upper end of the stalk cupshaped. The triphyllous pedicellariae (PL X. Fig. 17) 

 differ only little in shape from those of I r rechinus. - The pedicellariae of this species are upon the 

 whole few in number and little conspicuous. 



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



