122 ECHINOIDEA. I. 



niay be found to be so miicli the more iinportant, as the description of this species by Agassiz is 

 very unsatisfactory, and \ve have no figures of it at all. A primary tnbercle is fonnd on all the 

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

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

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

 cellariæ; a few small bihamate spicules in the buccal membrane. No spines on the buccal piates. 

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

 test not large, but very distinct. The globiferous pedicellariæ are as in SphærccJiiuus^ but here no 

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

 Figs. 8, g, 15); Ijetween the two former of these transitions ma}- perhaps be foiTud, while no transi- 

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

 \-erse series. The ophicephalous and triphyllous pedicellariæ of the common form. The spicules 

 in the globiferous pedicellariæ (PI. XXI. Fig. 14. b) are chiefly as in Spliærccliiuus, only more length- 

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

 form (PI. 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 

 Sfroj/gyloccntrot7is-s]iec{Qs mentioned above. Its nearest relation, no dotrbt, is Sp]iærccliiiiits\ 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 Sphærechinus impossible, as in the latter no indication of sucli 

 an e.xtension is found. The form is also very different from the high form of Sphærfchiiins. The 

 slits of the test, on the other hånd, are scarcelj- to be used as a distinguishing mark, as they are not 

 much smaller than in specimens of Spliærccli. graiiularis of a corresponding size. A new genus must 

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



Sfrongyloccntrohis albus (Mol.). A primary tnbercle is found on all the ambulacral piates; on 

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

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

 piates, some of those outside the buccal piates thick, carrying pedicellariæ. No spines on the buccal 

 piates. The globiferous pedicellariæ are very similar to those of Parcchimts miliaris etc, but the apo- 

 physis ends far from the edge of the blade (PI. 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 Str. drobachicnsis etc. The tridentate pedicellariæ are very peculiar (PI. XVII. 

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

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

 ophicephalous pedicellariæ are somewhat lengthened, but without conspicuous peculiarities; the tri- 

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

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

 of the tridentate and ophicephalous pedicellariæ is compact. The spictiles bihamate, very few in 

 number. 



With Str. albus must be classed the species gibbosits (Val.) and bullatus Bell. Witli regard to 



