ECHINOIUliA. II. rj 



ferous pedicellaricC |P1. X. Figs. 9, ii) are very cliaracteri.stic, the valves endiiio in a single long tooth, 

 at a right angle with the narrow blade, which forms a flattened, closed tnbe. As in Urechhms the 

 valves are clad with a thick, dark, e\idcntly glandular skin. Xoneck; the stalk is more compact than 

 in Ur'ecliiiiiis. In the two globiferous pedicellaritC I have seen, the valves are nns\ nnnetrically devel- 

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

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

 pedicellarise (PI. X. Fig. 26) have low and broad \alves, somewhat siniuite and \er\- finely and closely 

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

 cupshaped. The trideutate pedicellariae occur in two distinct forms; the one (PI. X. I-'ig. 22) has verv 

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

 of this widened part is closel\- serrate; in the lower, narrowed part the edge has oid\- 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 (FIX. Fig. 8) has the 

 blade almost, sometimes completel}', closed as a tube in the lower half; 

 the outer half is spoonshaped widened, with the edges fineh- 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 triiDhyllous pedicellarise (PL X. Fig. 14) are like those of 

 L'reck. gigimtnts, only somewhat more narrowed below the blade. — 

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

 feet as in Urrchi)nis. — The miliar\- spines as in Urecliiniix, very similar 

 to those of U. uarrsianus: I have not secured an^■ of the primarN' spines, ^'-- ^- -^'^''°^' P'^'™" °^ l"''"'""- 



echinus vesica; from the inside of 



SO that I cannot give any information of their structure. the test. Not dmwn with Camera. 



PilciiiatrcJiiiiHS vesica. The figures gi\en of the structure of the 

 actinal part of the test of this species in the Challenger -Report (PI. XXXV. 11--121 are not very 

 accurately drawn. The inner ambtdacral plates 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 by 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 plates (Fig. 6). 



The feature pointed out bv Agassiz as making a radical difference between Pilematechinus 

 and Cystechiuus. viz. that the labrum is followed by two plates in Piloiiatcchiuns. would indeed be 

 an extremely interesting fact, distinguishing this genus not onl\- from Cys f echinus (Urechinusj, but 

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

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

 of all recent Spatangoids. I was therefore \er> anxious to see, if P. vesica has the same primiti\-e 

 structure of the plastron. I had occasion to examine this question at a short visit to the British Mu- 

 seum this \-ear, and the result was that P. vesica does not show the ver\ primiti\e structure of the 

 plastron described by Agassiz for /'. Ratlibuiii. The labrum is very small, as shown in Fig. 6, 



7* 



