ECHINOIDEA. I. 



131 



pointed out more nearly. By an interpretation of tlie genera so confused as has been the case liere, 

 it is of course inipossible to liave a clear nnderstanding of the relation between theni. Of the char- 

 acters hitherto nsed anx greater importance can only be attribnted to one, viz. the deep slits in the 

 test (Troschel, Pomel). The genera with deep slits in the test prove to be all closely allied. Bnt 

 this character is no qnite reliable one; partly it is a matter of degree whether a slit is deep or not, 

 and especially there is the nnfortnnate circiimstance that the slits are always small in yonng speci- 

 mens, also in the species where the\" are deep in the adnlt ones; partly forms are fonnd with small 

 slits, which are, no donbt, most nearly allied to those with deep slits [Gyiiuirc/iiuiis). Then we have 

 left no other characters than the pedicellariæ and the spicnles, bnt they prove also to be excellent. 

 Of the pedicellariæ onh' the globiferous ones can be used for the gronping of the genera; the other 

 pedicellariæ are npon the whole very similar in all the forms treated here. 



The simplest form of globiferons pedicellariæ is evidently the one found in Ptirccliiiiits\ the 

 blade is open, the edges are not connected by cross-beams, not thickened, and project in two or more 

 rather long teeth on either side. A qnite similar form is fonnd in Loxcchiinis, only here a short neck 

 is fonnd, wliile Parccliiiius has no neck. — This form of pedicellariæ is only found in these two genera 

 which form accordingly a separate gronp ; the>- are \-ery similar as to habitus, so that nothing seems 

 to be found that might pre^'ent a pntting together of them. — A somewhat more complicate form is 

 found in the genera Echiiuis and Sfrrcchiitns. The edges of the blade are thickened, and are (with a 

 single exception: Stcrccli. Iiorridus and |rarel\-| Ecli. Alexaiidri) connected across the inside b\- more 

 or fewer cross-beams. One or more lateral teeth are found on either side, most freqnenth' there is a 

 tendencv to obliquit\- in the onter end of the blade, just below the end-tooth, and freqnently there are 

 two teeth on the strenger, a little projecting edge, and only one on the other, more straight edge. 

 This form of pedicellariæ is onh- fonnd in the two mentioned genera, and so they evidenth' form 

 another group; also the forms belonging here show considerable similarit\- as to habitus. — A similar 

 form of pedicellariæ is found, however, in one more genus, viz. Parncoitrotus; also here the edges are 

 thickened, with a tootli on either side, but the\' are not connected across the inside of the blade. It 

 seems that this genus, which is polypore and, with regard to habitus, very different from the other 

 genera mentioned here, must be interpreted as a somewhat farther relation of Ecliiuus and Stcrccliiiais. 

 In all these genera only simple bihamate spicitles are found. 



From these forms the development goes in two diverging directions: complete reduction of all 

 the lateral teeth , or strong development of the one unpaired lateral tooth. In PsaiiDi/rckiiuis, Toxo- 

 pncHstcs, Gyiinifc/iiiiits, Tripiieiistcs^ Splucrrchinus, Psciidobolctia^ and Psciidoccntrotus all lateral teeth 

 have disappeared, and the blade has become qiiite closed, tubular. Besides all these genera are distin- 

 guished by having small, tliick, more or less dumb-bell-shaped spicnles. There can be no doubt that 

 they form a separate group. The three first have regularly trigeminate pores, in Tripuciisfrs the 

 yonng individnals have also regularly trigeminate pores, but in the adult the pore areas extend so 

 much, that tlie\' look as if they were polypore; but they continue as a matter of faet to be oligopore. 

 Sphærcchinns and Pscudobolctia are polypore, mosth', however, with fonr pairs of pores in each are. 

 As the nppermost one in the series of development we find Psctidocentrofus with 5 — 6 pairs of pores 

 where the pore areas are even somewhat petaloid on the actinal side. 



17* 



