l'XIIINOIDRA. II. 



8 9 



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

 relationship to the Clypeastroids and Echinolampadae . ( 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 reallv been derived from one another in the direction here indicated. 



Plexeehinus 

 Cystechinus(?) 2 

 Pilematechinus 

 Urechinus 



Pourtalesia Echinosigra 



Spatagocystis Ceratophysa 



Cystocrepis Helgocystis 



Eehinoerepis 



Calymnidse Sternopatagus 



Stereopneustes 



Ananchytidae 



^< 



*t» 



•r*. 



«fg 



Clypeastroidea 



Collyritidae 



T3 

 >-i 

 o 



r-t- 

 O 

 in 



r-t 



n> 

 n 



P 

 So 



Holectypoidea 



SpatangidseJ 

 PateostoinatidDe 

 Palseopneustidse 

 Aeropidae 



Cassiduloidea 



Diademina 



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

 must form a small separate family reliee par Urechinus aux vrais Ananchytidce et rattaehee aux Spatangidce par Pa/aotropus 

 et Pkysasler . 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. 



-' This genus is quite insufficiently known and possibly does not really belong to this family. iComp. above p. 46, 49). 



3 Seusu latiori, comprising Spaiangina, Brissina etc. 



The Ingolf-Expedition. IV. 2. j2 



