ECHINOIDEA. II. 



actinal side, only a little shorter and clad with a thicker skin. The spines upon and around the peri- 

 stome are somewhat clubshaped (PI. IX. Fig. 39); the base of the primary spines is rather large; it 

 seems somewhat exaggerated in the Chall.-Ech. PL XXX. Fig. 20 the Fig. 21 of the same plate, 

 representing a miliary spine, according to the explanation of the plate, it is better not to speak of. 



In the specimen of -j-^ mm the primary tubercles form, on the abactinal side, an almost regular 

 vertical series in each row of plates, the tubercles being placed in the middle of the plates. In later 

 stages other tubercles grow larger than the primary ones, thus obscuring the vertical arrangement, 

 and it even sometimes looks as if the true primary tubercles have become resorbed 1 . 



In grown specimens the arrangement of the large tubercles is quite irregular, as described by 

 Agassiz. In the Challenger-Ech. p. 147 Agassiz remarks that in some specimens there may be 

 rudimentary bourrelets. I have seen the same thing. The Figures 10 and u, PI. VI represent the 

 actinal side of two specimens, one with a very distinct bourrelet, the other with scarcely a trace of it. 

 Also in U. giganteus this feature is found (Panamic Deep-Sea Ech. p. 155) though not so distinctly 

 developed, judging from the figure (PI. 73. i) to which reference is made. 



The tube-feet may be quite devoid of spicules, or with a single series of simple, somewhat spinous 

 rods with rounded ends (PL IX. Fig. 8) in the actinal, penicillate tube-feet as well as in the simple 

 abactinal feet; in the lower part of the tube-foot they are generally more irregular, more or less 

 branched. The peculiar fenestrate rods of the filaments have been figured by Loven (On Pourtalesia. 

 PL VIII. 56); they are, however, less fenestrate than shown there: No supporting skeletal plates are 

 found below the rods of the filaments in the actinal tube-feet. The frontal tube-feet are simple, without 

 a sucking disc (rosette), not differing from those of the other ambulacra. No large, specially developed 

 subanal tube-feet. 



Two sorts of pedicellariae are figured by Agassiz (Challenger-Ech. PL XXX. 22 24), viz. 

 tridentate (<large trifid longstemmed pedicellariae*) and ophicephalous (shorter roundheaded pedi- 

 cellarise, in the explanation of the plates called clubshaped pedicellarise with heavy-stemmed articula- 

 tion*). I find five different kinds of pedicellariae in this species, viz. globiferous, tridentate (two sorts), 

 tnphyllous and ophicephalous pedicellariae. 



The globiferous pedicellariae (PL IX. Fig. 35) have a rather conspicuous cap of evidently glan- 

 dular skin, thickening especially over the point of the valves. The latter (PL IX. Fig. 9) are very char- 

 acteristic; the blade is a closed tube ending in a large opening surrounded usually by nine long, 

 slender gracefully curved teeth, one of which is median in the outer edge. The basal part is large, 

 rounded; no neck. The stalk consists of long, thin calcareous fibres, connected only above and below; 



1 Agassiz (Panamic Deep-Sea Ech. p. 153, 15960, 166) has found such resorption to occur in Urechinus giganteus 

 and Cystechinus, as also in Pal&opneustes and Linopneustes; he sees therein a proof of the constant struggle that must exist 

 for the deposition of needed carbonate of lime . . . The least disorder in the growing tissue of any part of the test evidently 

 affecting at once the active deposition of the carbonate of lime of that regions. I may, however, remark that the tubercles 

 of these forms are very easily broken off. It is quite easy, as I have tried myself, in this way to produce all the different 

 stages of resorption > figured by Professor Agassiz (especially PI. 86. 2). The suggestion therefore does not seem unreason- 

 able that at least part of what Professor Agassiz thinks to be the result of a resorption is, indeed, only the result of the 

 animals having been badly rubbed- in the dredge or otherwise. That the empty place of such a primary tubercle may be 

 covered by a pigmented skin (as I have seen it very distinctly in a specimen of Pourtalesia Jeffreys!) is no proof of a res- 

 orption having occurred; it may as well be the result of some injury, by which the spine and tubercle was lost some 

 time before. 



The Ingolf-Expedition. IV. 2. 6 



