ECHINOIDEA. I. 



49 



Another very distiucth- marked group is formed by the species Asthcnosoma variuvi Gnibe, 

 Grubei Agass., iirciis Sarasin, and hrtcractis Bedford, all which species I have had occasion to 

 examine. The primary spines on the actinal side are CTirved, and end with a thin, but rather long, 

 little conspicuous hoof; the\- are green with dark rings. All the spines on the abactinal side and the 

 secondary ones on the actinal side are covered with skin; on the larger spines the bag of skin is 

 repeatedly constricted (Chall. Ech. PI. X\'I), on the small spines there is only a simple bag of skin at 

 the point (poison apparatus — Sarasin 350, 352); these skin-covered spines end in the usual point. 

 The tube feet are placed in three dense series; in the actinal tube feet a well developed sucking disk 

 is found. The sj^icules are small, irregularly branched, rarely with a single hole (PI. XI. Fig. 20); only 

 just below the sucking disk a few larger fenestrated plates are found. They are placed in 2 — 4 series, 

 but only in the outer part of the foot, nearest to the sucking disk; in the other, larger part of the 

 tube foot only quite few scattered spicules are found, and also in the abactinal tube feet only very 

 few spicules are found. This feature of the spicules also separates this grouj) of species very distiucth- 

 from all the other Echinothurids. 



The pedicellarice of these species are especially characteristic (while on the other hand there is 

 only very little difference in this respect between the species themselves). Only tridentate and tri- 

 phyllous pedicellarise are found here, but in return the tridentate ones are found in no less than three 

 well marked forms. In the largest form the blade is narrow, only widened in the point and provided 

 with 2 — 3 very coarse indentations which work into each other when the pedicellaria is shut; below 

 the blades are then wideh- separated; there are no fine teeth in the edge of the blade (PI. XIV. 

 Figs. 3, 7). Now, to be sure, I have only seen this form in A. variitin and Grubei^ but I think there 

 is no doubt that it is also found in the two others. There appears, besides, some difference between 

 A. varhim 2a\^ Gnibci ]ws>\ with regard to this form of pedicellarias, the\- being much slenderer in A. 

 varium than in the other; in both they have a length of 2— 2-2"'™ (the head). The neck is quite short. 

 — This difference in the pedicellarite of the two species indicates that A. Grubei is really a good 

 species, and not sj-nonymous with A. varhtiii^ as Agassiz is inclined to think (Chall. Ech. p. 84). 



The second, smaller form of tridentate pedicellarise (PI. XIII. Fig.s. 4, 27) reminds very much of 

 ophicephalous pedicellarice ; but as no indication of arcs is found here, there can be no question of 

 referring them to this kind; they are a highly modified form of tridentate pedicellariae. The blade is 

 short and broad, filled by a rich net of meshes, and with 2—3 large indentations in the edge, which is 

 otherwise .smooth as in the large form. When the pedicellaria is shut the blades join with the excep- 

 tion of a quite small space at the base. Also this form has a very short neck. The length of the 

 head 1-2 — 1-5™". This form as well as the following one and the triplnllous pedicellaria; are quite 

 identical in all four species. — On PI. XVI. Figs. 10 and 11 in the < Cliallenger»-Echinids Agassiz 

 gives tolerably recognizable figures of this and the following form of pedicellarice; — large, short- 

 stemmed* and small-headed, long-stemmed pedicellaria: they are called. PI. XEIV. Fig. 34 likewise 

 gives a rather good figure of a valve of the second tridentate form, and Fig. 36 of the third form, 

 which is here called < large-headed . But it would be difficult to .say what is meant by PI. XLII. 

 Fig. 9, and PL XLIII. Fig. 2, although the former is given as a dong-headed, long-stemmed», the latter 

 as a < long-stemmed, small-headed pedicellaria oi A. Grubri. On the other hand the pedicellaria 



The In^olf-Expedition. I\'. i. 7 



