I-;CHIXOII)RA. I. 



133 



plate, and these plates become much narrower than the t)tliers, but keep their three tube feet. This 

 development is carried on in Tripncustcs and Hcliocidaris, where the primary spine is wantinj^ in more 

 ambulacral plates after each other. Pa this development there is made room for far more tube feet than 

 when all the ambulacral plates are t>-pically developed and provided with a primarv tubercle; but 

 there are constantly only three tube feet for each compound ambulacral plate. Tlic same end is reached 

 by the fact that the ambulacral plates are made to consist of more than three prinuiry plates, 

 that the)- become polypore. In almost all the groups both oligopore and poh'pore forms prove to be 

 found; only Parasalcnia has no polypore relation, and in the Sfrongylocen(rohcs-gxo\\Y> 'i" oligopore 

 form is still wanting. It may not be thought unreasonable to expect that such a one will be found; 

 it is no far cry from Sfr. piilcherririms where ouly four pairs of pores are found. 



Anthocidaris Strongyloceutrotus 



Parasalenia 



Paracentrotns 



Pseudocentrotus 



Pseudoboletia 



Sphserechinus 



Tripueustes 



Toxopneustes 



Gymuechiuus 



Psammechinus 



Sterechinus 

 Echinus 



Colobocentrotus 

 Heterocentrotus 

 Echinometra 

 Toxocidaris 

 Echinostrephus 

 Heliocidaris 

 Pseudechinus 



Loxechinus 



Stomopneustes 



Parechinus 



The result of the studies of Echhiomctyadcr and Triplcchiiiido- represented here, is expressed 

 m the following- systeui. 



Fam. Stomopneustidae n. fam. 



The spicules irregular, more or less tubular fenestrated plates. The globiferous pedicellariai 

 ■without end-tooth ') The stalk compact. 



Only one geuus known. 



Stomopneustes Ag. 



The pores trigeminate. Only every fourth or fifth ambulacral plate with primary tubercle, but 

 this tubercle is large and spreads over several ambulacral plates. The sj^ines long and thick; small 

 spines on the buccal plates. The buccal membrane w-ith numerous fine fenestrated plates, quite im- 

 bedded in the skin. The gills with numerous three-radiate spicules. A deep furrow along the median 

 line in the interambulacral areas. 



M Perhaps here may be found, besides the large globiferous pedicellarite without end-tooth laud without poison 

 gland?), a smaller form of globiferous pedicellariEe of the common structure. (See above p. 126J. 



