ECHINOIDEA. II. 



51 



ferous pedicellariæ (PI. X. Figs. 9, 11) are very characteristic, the valvcs ending in a single long tootli, 



at a right angle with the narrow blade, which form.s a flattened, closed tube. A.s in Urcclii)iits the 



valves are clad with a thick, dark, evidently glandular .skin. No neck; the stalk is more compactthan 



in Vrrcliiniis. In the two globiferous pedicellariæ I have seen, the valves are unsymmetrically devel- 



oped in the basal part, the one figured from the inside being the most regular of them. Whether this 



is a constant feature it is, of course, impossible to decide from such scanty material. The ophicephalous 



pedicellariæ (PI. X. Fig. 26) ha\-e low and broad valves, somewhat sinuate and ver)' fineh- and closely 



serrate along the edge of the blade down to the apophysis. The upper end of the stalk as usual 



cupshaped. The tridentate pedicellariæ occur in two distinct forms; the one (PL X. Fig. 22) has very 



long and narrow vah'es, somewhat widened in about the outer third, where the \-al\-es join. The edge 



of tilis widened part is closely serrate; in the lower, narrowed part the edge has onh' some ver\' few 



small thorns. The blade is open along the whole length ; there may be a faint indication of a meshwork 



in the blade. This form reaches a length of ca. 1-2'"™ (head). The other form (PI. X. Fig. 8) has the 



blade almost, sometimes completely, closed as a tube in the lower half; 



the outer half is spoonshaped widened, with the edges fineiy serrate. 



In smaller specimens the narrowed part of the blade is shorter, in quite 



small ones it is not narrowed at all, the blade being simply leaf-shaped. 



This form is much smaller than the former, the largest ones seen being 



ca. 0-5""". The trijjhyllons pedicellariæ (PI. X. Fig. 14) are like those of 



Urech. gigcnitnis, only somewhat more narrowed below the blade. — 



The spicules and the rods supporting the filaments of the actinal tube- 



feet as in Urfcliiriiis. — The miliary spines as in Urechiinis. very similar 



to those of U. narrsmiuts; I have not secured anv of the primarN' spines, ^'S' ''• •^'^''°^' P'^^^™" oi P.lemai- 



echinus vesica; from the inside of 



so that I cannot give any information of their structure. the test. Not drawn with Camera. 



Pilcmnfcchiniis vesica. The figures given of the structure of the 

 actinal part of the test of this species in the Challenger -Report (PI. XXX\'. 11 — 12) are not very 

 accurately drawn. The inner ambulacral piates are represented as being in contradiction to the general 

 rule of La, II. a, III. b, IV. a, V. b having two pores; this is not really the case, they are fairly in 

 accordance with the rule, as I have been able to determine in the British Museum b\- the examination 

 what seems to be the original preparation after which the two cited figures are drawn. I give here a 

 sketch of the actinal plastron and adjoining ambulacral piates (Fig. 6). 



The feature pointed out by Agassiz as making a cradical difference, between Pileniatcchtmis 

 and C\stechinits, viz. that the labrum is followed b\- two piates in PHcniafcclii)iiis. would indeed be 

 an extremeh' interesting faet, distinguishing this genus not onh' from Cystcchiiius { Urecliiiiiisj. but 

 upon the whole from all the Meridosternata. Onl\- in the Dysasfcridæ (and the Cassidnlids) is a similar 

 structure of the odd interambulacrum found. Pilotiatcclihuts would then represent the most primitive 

 of all recent Spatangoids. I was therefore very anxious to see, if P. vrsica has the same primiti\'e 

 structure of the plastron. I bad occasion to examine this question at a short \-isit to the British AIu- 

 seum this \-ear, and the result was that P. vrsira does not show the ver>- primitive structure of the 

 plastron described by Agassiz for P. Ratlihuui. The labrum is very small, as shown in Fig. 6, 



f 



