ECHINOIDEA. II. 



ferons pedicellarise (PI. X. Figs. 9,11) are very characteristic, the valves ending in a single long tooth, 

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

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

 in Urechinus. In the two globiferous pedicellarise 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 

 pedicellariae (PI. X. Fig. 26) have low and broad valves, somewhat sinuate and very finely and closely 

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

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

 long and narrow valves, somewhat widened in about the outer third, where the valves join. The edge 

 of this widened part is closely serrate; in the lower, narrowed part the edge has only some very 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. i-2 mm (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 finely 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 triphyllous pedicellarise (PI. X. Fig. 14) are like those of 

 Urech. gigantrits, only somewhat more narrowed below the blade. 

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

 feet as in Urechinus. - - The miliary spines as in Urechinus, very similar 



to those of V.narcsianus; I have not secured anv of the primary spines, Fig ' 6 ' Actinal plastron of 



echinus vesica; from the inside of 



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



Pilemat echinus vesica. The figures given of the structure of the 



actinal part of the test of this species in the Challenger -Report (PI. XXXV. n 12) are not very 

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

 rule of I. a, 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 by Agassiz as making a radical difference* between Pilemat echin its 

 and Cystechinus, viz. that the labrum is followed by two plates in Pilemat echinus, would indeed be 

 an extremely interesting fact, distinguishing this genus not only from Cystechinus (Urechinus), but 

 upon the whole from all the Meridosternata. Only in the Dysasterida (and the Cassidulids) is a similar 

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

 of all recent Spatangoids. I was therefore very anxious to see, if P. vesica has the same primitive 

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

 seum this year, and the result was that P. vesica does not show the very primitive structure of the 

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



7* 



