122 ECHINOIDEA. I. 



may be found to be so much the more important, as the description of this species by Agassiz 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 only 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 pedicellariae are as in Spk&reckmus , but here no 

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

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

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

 verse series. The ophicephalous and triphyllous pedicellarise of the common form. The spicules 

 in the globiferous pedicellarise (PL XXI. Fig. 14. b) are chiefly as in Sphcrrechinus, only more length- 

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

 form (PL XXI. Fig. 14. a); 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 

 Strongylocentrotus-sipeci&s mentioned above. Its nearest relation, no doubt, is Spharcchimis; but it 

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

 actinal side renders the referring to Sphat -echinus impossible, as in the latter no indication of such 

 an extension is found. The form is also very different from the high form of Sph<rrechinus. 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 Sphcerech. gramilaris of a corresponding size. A new genus must 

 be formed for this species, and for this genus I propose the name of Pseudocentrotus. 



Strongyloccntrotus 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 pedicellariae. No spines on the buccal 

 plates. The globiferous pedicellarise are very similar to those of Parechimis miliaris etc., but the apo- 

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

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

 and stretched out as in Sir. drobachicnsis etc. The tridentate pedicellarise are very peculiar (PL XVII. 

 Fig. 1 8), with a keel in the middle of the blade, which is short and narrow; the point is a little 

 widened with 34 strong teeth on either side. There are no transverse series of small teeth. The 

 ophicephalous pedicellarise are somewhat lengthened, but without conspicuous 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 ophicephalons pedicellarise is compact. The spicules bihamate, very few in 

 number. 



With Sir. albus must be classed the species gibbosus (Val.) and bullattis Bell. With regard to 



