ECHINOIDEA. I. j,i 



pointed out more nearly. B>- an interpretation of the ji^enera so confused as has been the case liere, 

 it is of course impossible to have a clear unilcrstanding of the relation between them. Of the char- 

 acters hitherto used any o^reater importance can onl\- ])e attributed to one, viz. the dee]) slits in the 

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

 this character is no quite reliable one; partl\- it is a matter of degree whether a .slit is deep or not, 

 and especialh- there is the unfortunate circumstance that the slits are always small in voung speci- 

 mens, also in the species where the\- are deep in the adult ones; partly forms are found with small 

 slits, which are, no doubt, most nearly allied to those with deep slits (GyiiD/rc/iiinis). Then we have 

 left no other characters than the pedicellariae and the spicules, but the}- pro\e also to be excellent. 

 Of the pedicellarise only the globiferous ones can be used for the grouping of the genera; the other 

 pedicellariae are upon the whole \-ery similar in all the forms treated here. 



The simplest form of globiferous pedicellarite is evidenth- the one found in Parcchi)iiis\ 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 quite similar form is found in Loxccliiims, onl\- here a short neck 

 is found, while Parcchinus has no neck. — This form of pedicellarise is only found in these two genera 

 which form accordingly a separate group; the\- are very similar as to habitus, so that nothing seems 

 to be found that might prevent a putting together of them. — A somewhat more comislicate form is 

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

 single exception: Stcrccli. horrid us and | rarely | Ecli. Alexandri) connected across the inside b\' more 

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

 tendeucN" to obliquit\ in the outer end of the blade, just below the end-tooth, and frequently there are 

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

 This form of pedicellaris is only found 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 pedicellarite is found, however, in one more genus, viz. Paraccntrofiis\ also here the edges are 

 thickened, with a tooth on either side, but they 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 Echinus and Sterechinits. 

 In all these genera only simple biharaate spicules are found. 



From these forms the development goes in two di\-erging directions: complete reduction of all 

 the lateral teeth, or strong development of the one unpaired lateral tooth. In PsanDiirchiiius, Toxo- 

 pncusfcs, Gyiinicchiiius, Tripiicustcs, SpJiccrccliiuus, Pscudobolrtia^ and Pscudocriiirofus all lateral teeth 

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

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

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

 young individuals have also regularly trigeminate pores, but in the adult the pore areas extend so 

 much, that they look as if they were polypore; but they continue as a matter of fact to be oligopore. 

 Sphcrrrchinus and Pscudobolctia are polypore, mostly, however, with four pairs of pores in each arc. 

 As the uppermost one in the series of development we find Pscudoccntrohis w'ith 5 — 6 pairs of pores 

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



17* 



