ECHINOIDEA. I. 



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

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

 acters hitherto used any greater importance can only be attributed 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. Hut 

 this character is no quite reliable one; partly it is a matter of degree whether a slit is dee]) or not, 

 and especially there is the unfortunate circumstance that the slits are always small in young speci- 

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

 slits, which are, no doubt, most nearly allied to those with dee]) slits [Gymnechinus). Then we have 

 left no other characters than the pedicellarise and the spicules, but they prove also to be excellent. 

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

 pedicellarise are upon the whole very similar in all the forms treated here. 



The simplest form of globiferous pedicellarise is evidently the one found in Parechinus\ 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 Loxechinus, only here a short neck 

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

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

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

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

 single exception: Sterech. horridus and |rarely| Ech. Alexandri) connected across the inside by more 

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

 tendency to obliquity 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 pedieellarue is only found in the two mentioned genera, and so they evidently form 

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

 form of pedicellarise is found, however, in one more genus, viz. Paracentrotus; 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 Stcrcchhnis. 

 In all these genera only simple bihamate spicules 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 Psammeckinus, Toxo- 

 pneustes, GymnecMnus, Tripneustes, Sphmrechinus, Pseudodoletta, and Pseudocentrotus 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 Tripneustes 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. 

 Spharechinus and Pseudoboletia are polypore, mostly, however, with four pairs of pores in each arc. 

 As the uppermost one in the series of development we find Pseudocentrotus with 5—6 pairs of pores 

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



