ECHINOIDEA. II. 



understand the true relationship not only of many aberrant groups of Spatangoids, but also their 

 relationship to the Clypeastroids and Echinolampadse. (Chall.-Ech. p. 148). 



I give here a graphic representation of the mutual relationship of the Spatangoids, as I under- 

 stand it. It will be seen that my view of the Meridosternata is in rather close accordance with that 

 represented in the tabular view of the Meridosterni given by Lambert 1 I may notice expressly that 

 it is not meant as a genealogical tree of the genera. As for the families, I do not doubt that they 

 have really been derived from one another in the direction here indicated. 



Plexechinus 

 Cystechinus(?) 2 

 Pilematechinus 

 Urechinus 



Pourtalesia Echinosigra 



Spatagocystis Ceratophysa 

 Cystocrepis Helgocystis 



Echinocrepis 

 Calymnidse Sternopatagus 



Spatangidse 3 

 Palseostomatidse 

 Palaeopneustidse 

 Aeropidse 



Stereopneustes 



Ananchytidse 



Clypeastroidea 



Cassiduloidea 



Holectypoidea 



Diademina 



1 Etudes morph. sur le plastron ties Spatangides. As for Lambert's remark (Op. cit. p. 93) that the Pourtalesiae 

 must form a small separate family reliee par Urechinus aux vrais Atmnchytidce et rattachee aux Spatangidce par Pa/ceotropus 

 et Physaster, I must refer to the above remarks against seeking transitions between the Pourtalesiae and the Amphisternata. 

 Lambert is here, evidently, in disaccord with the views otherwise expressed throughout that excellent paper. 



2 This genus is quite insufficiently known and possibly does not really belong to this family. (Comp. above p. 46, 49). 



3 Sensu latiori, comprising Spa/angina, Rrissina etc. 



The Ingolf-Kxpedition. IV. 2. 12 



