122 ECHINOIDEA. I. 



may be found to be so ninch the more important, as the description of this species by A gas si z is 

 very unsatisfactory, and we have no figures of it at all. A primary tubercle is found on all the 

 ambulacral plates; the pore areas of the actinal side are much extended, a little petaloid; the two lower- 

 most plates have onh- three pairs of pores. Two ocular plates reach to the periproct. The buccal mem- 

 brane contains numerous lengthened fine fenestrated plates, only a few are complicate and carry pedi- 

 cellarise; a few small bihamate spicules in the buccal membrane. No spines on the buccal plates. 

 The gills contain the usual irregular fenestrated plates, but no bihamate spicules. The slits of the 

 test not large, but very distinct. The globiferous pedicellaria; are as in SpJicprccliums^ but here no 

 glands are found on the stalk. The tridentate pedicellarise occur in three different forms (PI. XXI. 

 Figs. 8, 9, 15); between the two former of these tran.sitions may perhaps be found, while no tran.si- 

 tional forms seem to be found between the latter two. The teeth on the edge form no trans- 

 verse series. The ophicephalous and triphyllous pedicellaria; of the connnon form. The spicules 

 in the globiferous pedicellariae (PI. XXI. Fig. 14. b) are chiefly as in SplKPrechinus^ o\\\\ more length- 

 ened; those of the tube feet are rather much branched, but they belong, however, to the bihamate 

 form (PI. XXI. Fig. 14.3); they are numerous in the abactinal tube feet, but very few in number in the 

 actinal ones. 



It is evident from the features mentioned here that this species is not closely allied to the 

 Sirongylocentrotus-s^ecits mentioned above. Its nearest relation, no doubt, is Sphcercchimis; but it 

 cannot be referred to this genus eitlier; especially the strong extension of the pore areas on the 

 actinal side renders the referring to Spkcerechinus impossible, as in the latter no indication of such 

 an extension is found. The form is also very different from the high form of Spha-rcchiims. The 

 slits of the test, on the other hand, are scarcely' to be used as a distinguishing mark, as they are not 

 much smaller than in specimens of Sphcerecli. graimlaris of a corresponding size. A new genus must 

 be formed for this si^ecies, and for this genus I pi'opose the name of Pseudocentrotus. 



Stroiigyloccntrotus albus (Mol.). A primary tubercle is found on all the ambulacral plates; on 

 the lowermost ones there are only three pairs of pores. One ocular plate reaches to the periproct, 

 the others almost reach it. The buccal membrane with numerous, rather large, lengthened fenestrated 

 plates, some of those outside the buccal plates thick, carrying pedicellarise. No spines on the buccal 

 plates. The globiferous pedicellarise are very similar to those of Parechinus viiliaris etc., but the ajxi- 

 physis ends far from the edge of the blade (PI. XVII. Fig. 5); there is a short, but distinct neck, onlv, 

 however, containing longitudinal muscles, not also circular nniscles, so that it cannot be retracted 

 and stretched out as in Sir. drobachicnsis etc. The tridentate pedicellarise are very ])eculiar (PI. XVII. 

 Fig. 18), with a keel in the middle of the blade, which is short and narrow; the point is a Httle 

 widened with 3 — 4 strong teeth on either side. There are no transverse series of small teeth. The 

 ophicephalous pedicellaria; are somewhat lengthened, but without con.spicuous peculiarities; the tri- 

 phyllous pedicellarise of common form. The stalk of the globiferous and triphyllous pedicellarise 

 consists of long, slender calcareous threads, almost only connected at the ends of the stalk; the stalk 

 of the tridentate and ophicephalous pedicellariae is compact. The spicules bihamate, ver\- few in 

 number. 



With Str. nlhus must be classed the species gihbosus (Val.) and bullatns Bell. With regard to 



