ECHINOIDEA. I. 



J 33 



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

 development is carried on in Tripneustes and Heliocidaris, where the primary spine is wanting in more 

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

 when all the ambulacral plates are typically developed and provided with a primary tubercle; but 

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

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

 that they become polypore. In almost all the groups both oligopore and polypore forms prove to be 

 found; only Parasalenia has no polypore relation, and in the Strongylocentrohis-growp an 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 Sir. pulcherrimus where only four pairs of pores are found. 



Anthocidaris Strongylocentrotus 



Parasalenia 



Paracentrotus 



Stomopneustes 



Pseudocentrotus 



Pseudoboletia 



Sphasreehinus 



Tripneustes 



Toxopueustes 



( rynmechiuus 



Psammechinus 



Sterechinus 

 Echinus 



Parechinus 



Colobocentrotus 

 Heterocentrotus 

 Echinometra 

 Toxocidaris 

 Kehiuostrephus 

 Heliocidaris 

 Pseudechinus 



Loxechinus 



The result of the studies of Echinometrada and Triplechinida represented here, is expressed 

 in the following system. 



Fam. Stomopneustidae n. fam. 



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

 without end-tooth 1 ) The stalk compact. 



Only one genus 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 spines long and thick; small 

 spines on the buccal plates. The buccal membrane with 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. 



») Perhaps here may be found, besides the large globiferous pedicellariae without end-tooth land without poison 

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



