ECHINOIDEA. II. 



89 



understand the true relationship not only of niany aberrant groups of Spatangoids, liut also tlieir 

 relationship to the Clypeastroids and Echinolampadæ \ (■ Cliall. -Ech. p. 148). 



I give liere a graphic representation of the niutual relationship of the Spatangoids, as I under- 

 stand it. It will be seen that m\- view of the Mcridostcriiaia is in rather close accordance with that 

 represented in the tabular view of the Mcridostcriii given by Lambert." I nia\- notice expressly that 

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

 have reallv been dcrived from one another in the direction hcre indicated. 



Plexechinus 

 Cystechinns(?)- 

 Pileniatechinus 

 Urechinus 



Pourtale.sia Echinosigra 



Spatagocystis Ceratophysa 



C3stocrepis Helgoc)stis 



Echinocrepis 



Calymnidæ Sternopatagus 



^~ 



%\ Stereopneustes 



Ananchytidæ 



CoUyritidæ 



Clypeastroidea 



o 



O 



Holectypoidea 



Spatangidæ 3 

 Palæostomatidæ 

 Palæopneustidæ 

 Aéropidæ 



Cassiduloidea 



Diadeniina 



' Etudes morph. sur le plastron <les Spatangides. As for Lambert' s remark (Op. cit. p. 93) tliat the Poiirtalesiæ 

 must form a small separate family ■ reliée par Urechinus aux vrais Annncliylidæ et rattachée aux Spatangidæ par Pa/iro/rofius 

 et Pliysasler>, I must refer to the above remarks agaiust seeking trausitions between the Pourlalesiæ aud the Amphisternata. 

 Lambert is here, evideiitly, in di.saccord 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, coniprisiiig Spn/angina, Brissina etc. 



The logolf-Expedition. IV. 2. ,„ ■ 



