ECHINOIDEA. II. 



41 



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

 stome are somewhat clnbshaped (PI. IX. Fig. 39); the base of the [iriniarx spines is rather large; it 

 seems somewhat exaggerated in the Chall. -Kch. PI. XXX. l-'ig. 20 — the P"ig. 21 of the .same plate, 

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



In the specimen of 7-5""" the primary tubercles form, on the al)actinal side, an almost regular 

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

 stages other tubercles grow larger than the primar\- ones, thus obscuring the vertical arrangement, 

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



In grown specimens the arrangement of the large tubercles is quite irregular, as described b\- 

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

 rudimentar\- bourrelets. I have seen the same thing. The Figures 10 and 11, PI. \'I represent the 

 actinal side of two specimens, one with a \er\- distinct bourrelet, the other with scarceh' a trace of it. 

 Also in U. gigaiifcus this feature is found (Panamic Deep-Sea Ech. p. 1551 though not so distincth' 

 de\-eloped, judging from the figure (PI. 73. i) to which reference is made. 



The tube-feet may be quite de\'oid of spicules, or with a single series of simple, somewhat spinous 

 rods with rounded ends (PI. 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 Ponrtalesia. 

 PI. VIII. ;,6); the\- are, however, less fenestrate than .shown there. Xo 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, specialh- de\-eloped 

 subanal tube-feet. 



Two sorts of pedicellarite are figured by Agassiz («Challengera-Ech. PL XXX. 22 — 24), \iz. 

 tridentate ( large trifid longstemmed pedicellarise ) and ophicephalous (shorter roundheaded pedi- 

 cellariae , in the explanation of the plates called clnbshaped pedicellariae with heavy-stemmed articula- 

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

 tnph>llous and ophicephalous pedicellaricC. 



The globiferous pedicellariae (PI. 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 onh- above and below; 



I Agassiz (Pauainic Deep-Sea Ech. p. 153, 159—60, 166) has found such resorption to occur in Vrechinus giganleus 

 and Cystechinus, as also in Pce/aopueus/es and Linopneustes; he sees therein a proof of < the constant struggle that must exist 

 for the deposition of needed carbonate of Hme> ... «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 regionw. 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 <iresorption;> figured bv Professor Agassiz (especially PI. S6. 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 ma}' be 

 covered by a pigmented skin (as I have seen it verj' distincth- in a specimen of Pouitalcsia Jeffreysi) is no proof of a res- 

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

 time before. 



The Inuolf-Expedition. IV. 2. 6 



