ECHINOIDEA. I. 



133 



plate, and these piates become nnicli iiarrower tlian the others, but keep their three tube feet. Tliis 

 development is carried 011 in Tripnciistcs and Hrliocidaris, where the priman- spine is wanting in more 

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

 when all the ambnlacral piates are typically developed and provided with a primarv tubercle; but 

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

 by the faet that the ambnlacral piates are made to consist of more than three primary piates, 

 that they become polypore. In almost all the gronps both oligopore and poh'pore forms prove to be 

 fomid; onh- Parasalcnia has no polypore relation, and in the Strollgylocclltl■ot^^s-gro\\^^ an oligopore 

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

 it is no far cr\- from Str. pitlclicrriiiius where only four pairs of pores are found. 



Anthocidaris Strongjlocen trotus 



Parasalenia 



Psendocentrotus 



Pseudoboletia 



Sphærechinus 



Tripneustes 



Toxopneustes 



Gynmechinus 



Psammechinus 



Paracentrotus 



Stomopneustes 



Sterechinus 

 Echinus 



\ ! 



■.,j 



Parechinus 



Colobocentrotns 

 Heterocentrotus 

 Echinonietra 

 Toxocidaris 

 Echinostrephus 

 Heliocidaris 

 Pseudechinus 



Loxechinus 



The result of the studies of Ecf/ii/oijufrada- and Triplcchinidæ represeuted here, is expressed 

 in the followiug system. 



Fam. Stomopneustidæ n. iam. 



The spicules irregular, more or less tubular fenestrated piates. The globiferous pedicellariæ 

 without end-tooth") The stalk compact. 



Only one genus known. 



Stomopneustes Ag. 



The pores trigeniinate. Only every fourth or fifth ambnlacral plate with primary tubercle, but 

 this tubercle is large and spreads over several ambnlacral piates. The spines long and thick; small 

 spines on the buccal plate.s. The bnccal membrane with numerous fine fenestrated piates, quite im- 

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

 line in the interambulacral areas. 



M Perhaps here mav be found, besides the large globiferous pedicellariæ without end-tooth (and without poison 

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



