226 M. A. Pomel on the Classification of Echiiiida. 



and the obovate form mask the radial symmetry for the be- 

 nefit of the bilateral. The second have the mouth central or 

 nearly so, the ambulacra similar, and the anus more or less 

 posterior, but often mounting high enough to enter into the 

 series of the genital pieces, which open behind to receive it. 

 The third have the mouth central and the anus opposite, 

 always completely enclosed by the genital apparatus. This 

 division appears to us more natural than the division into 

 two groups of regular and irregular forms, the distinctive 

 character of which is not so absolute as it has been repre- 

 sented. 



The Spatiformes or Spatango'ides form two groups, according 

 as their ambulacra are constituted by simple pores throughout 

 their whole extent {Ananchytida) ^ or as these ambulacra are 

 petaloid [8patangi). The homogeneity of the family of true 

 Bjpatangi is such that no one has yet supposed that it could 

 be subdivided; however, an attentive study permits us to 

 recoo:nize and even to define in it several new well-marked 

 groups. 



1. The Ewpatagia have the madreporic tubercle prolonged 

 behind between the ocellar pieces in the place of the unpaired 

 genital plate ; their petals are even with the test, and provided 

 on the interporiferous area with tubercles like those of the 

 other areas ; we may further separate in it the type with an 

 internal fasciole {Breynia), that with lanceolate petals [Ewpa- 

 tagus)j and that with sublinear petals {Trachyspatagus) . 



2. The Brissia are like the foregoing, as far as the ma- 

 dreporide goes ; but their petals are depressed, well-defined, 

 and with an interporiferous zone provided only with granules. 

 Some have the tubercles of the back heterogeneous {Leskia) ; 

 others have them almost homogeneous, and their periprocta is 

 remarkably open [Brissus) ; others have some small, oblique, 

 closely approximated dorsal tubercles and a moderate peri- 

 procta {Brissopsis). 



3. The Micrasteria have the apical apparatus compact — 

 that is to say, with the madreporic tubercle in the centre of 

 the genital plates, which are contiguous. The tubercles of the 

 back are most frequently scattered amidst an abundant granu- 

 lation. The ambulacra are depressed and well defined. Al- 

 most all the genera have fascioles. 



4. The Toxasteria have the apex compact, and some 

 scattered dorsal tubercles ; but their petals are even with the 

 test, and the anterior ambulacrum has linear pores, either 

 alone or mingled with round pores. The peristome is not so 

 boldly labiated as in the other Spatangoi'des. There are no 

 fascioles. 



