64 ECHINOIDEA. II. 



other side, evidently the inner plate of interatnbulacra i and 4 (PI. VIII. Fig. 1), as it is also found 

 sometimes in P. Jeffreys/. Upon the whole the structure of the actinal side, labrnm, sternum, episternnm, 

 the two ambulacra of the bivinm and the postero-lateral interambulacra agree very nearly with that 

 of /'. Jeffreys/. The periproct differs a little in outline from that of Jeffreys!, being more elliptical, not 

 abruptly widened in the upper part as in that species. The plates surrounding the periproct are 5. a. 

 6—8 and b. 7— 9; this holds good also for younger specimens, whereas in smaller specimens of P. Jef- 

 freys/ (till at least a size of 3o ram ) there are 4 epiproctal plates on each side (5. a. 5 — 8 and b. 6— 9) (in 

 larger specimens there are only three epiproctal plates as in P. Wandeli, the lower pair being shut 

 off from the periproct). The apical system (PI. VIII. Figs. 2, 7) as in Jeffreys!, perhaps a little closer 

 to the anterior border than in that species. I have found a case of the genital plates being distinct 

 (PL VIII. Fig. 2) as found exceptionally by Loven in Jeffreys/ (in that species I have not met with 

 such a case). 



The tuberculatum shows some difference from P. Jeffreys/. The linear arrangement of the pri- 

 mary tubercles is in larger specimens more prominent than in that species. The iuterambulacral plates 

 at the front sides (posterior series of interambulacra 2 and 3) each bear two prominent parallel or 

 posteriorly a little diverging, series of primary tubercles; on the uppermost and lowermost 2 — 3 plates 

 of this series the linear arrangement of the tubercles is indistinct. The part of these plates, which is 

 bent over on the front edge, bears only few, irregularly arranged primary tubercles, as is also the case 

 with the other plates on the front. The following two series of plates (ambulacra II and IV, a. b.) bear 

 a series of primary tubercles each. Also the following iuterambulacral plates show a tendency towards 

 a serial arrangement of the tubercles. In these series the tubercles always increase in size from before 

 towards the posterior end, the hinder one being the largest. It is only the plates on the sides of the 

 test which have the tubercles thus serially arranged. The rest of the test has like P. Jeffreys/ only 

 irregularly scattered primary tubercles, somewhat less numerous, however, than in that species. The 

 miliarv tubercles are upon the whole less numerous than in feffreysi, the test looking more smooth 

 than is generally the case in that species. The sutures are not elevated as in Jeffreys!. - Though the 

 serial arrangement of the primary tubercles is much more prominent in P. Wandeli than in Jeffreys/, 

 when larger specimens are compared, it must be conceded that in smaller specimens the serial arrange- 

 ment is almost equally developed in both species. 



The primary spines of the abactinal side are very long, especially those of the anterior series 

 of the antero-lateral ambulacra and those of the iuterambulacral plates on the front edge, and — in 

 accordance with the size of the tubercles — the posterior spine of each series is the longest. The 

 longer of these spines reach from the anterior end of the test to the periproct, thus reaching more 

 than two thirds of the length of the test. They are curved and bent backwards, lying rather close to 

 the test; generally they are strongly thorny, especially along the convex side, which gives them a 

 characteristic lustre. Sometimes they are irregularly curved at the point. (PI. V. Figs. 1, 3, 5. PL XI. 

 Fig. 36). These long spines give this species a very characteristic appearance, differing highly from 

 P. Jeffreys/ in which species the spines are much shorter, smooth, and generally not bent backwards 

 over the test. (Comp. PL V. Figs. 1, 3, 5 with PL V. Figs. 19, 21, 23). — The spines of the actinal plastron 

 (PL XI. Pig. 35) are flattened at the point, like those of Jeffreys/, and likewise those within the invagi- 



