PALEOPNEUSTES AND LIX0PXEUSTE8. 



171) 



Something 



the former tliere are always four genital p(;ro,s, in the latter sometimes 

 three, Fig. '2G1. Amphipneustes, like Paleopneustes, lias no subanal 

 fasciole. Koehler also says ' it has no marginal fasciole. The swollen coronal 

 plates, as in Stenonia, are a most interesting feature of the genus. No trace 

 of this is apparent in either Paleopneustes or Linopneustes. 

 of the kind is found among the Brissinso in 

 Hemiaster. Amphipneustes is also marked for 

 the great development of the pli3dlodes ; ^ they 

 are as well defined as in Paleopneustes cristalus. 



The genera Phrissocystis, Paleopneustes, 

 Linopneustes, and Amphipneustes are interest- 

 ing from the combination of structural features 

 they possess, showing in one direction quite re- 

 cent Spatangoid characters, like those of the 



laterally elongate actinostome. Figs. 263, 264, fig. 262. paleopne.stks hystkix. 

 with a powerful labium (Pis. 92, 95, 96, 97), 



the great development of the phyllodes, broad actinal lateral ambulacral 

 zones, a well developed plastron, especially in Linopneustes, and a compact 

 apical system (Pis. 93, fig. 1 ; 94, fig. 7), while the structure of the abactinal 

 part of ^the ambulacra is related to more ancient types with which is asso- 

 ciated also a more primitive arrangement of the plates surrounding the 

 actinal system. 



We may look upon the presence of a marginal fasciole (PI. 94, fig. 1), as 

 an early or rudimentary peripetalous fasciole of a stage of development in 



110 mm. 



Fio. 263. Linopneustes longispinus. 



82 mm. 



Fig. 264. Linopneustes loncjispinus. 



which the petals are not as yet defined as in the more recent Spatan- 

 goids ; while the presence of a well defined subanal fasciole in Linopneustes 

 (PI. 92) is an additional link connecting it with the more recent Spatangoids.^ 



• Koehler, "Belgica" Echinides et Ophiuies, p 11. 



2 Koehler, loc. cit. PI. V, fig. 3G. 



8 The classification of tlie Spatangoids according to the presence or absence of the subanal fasciole 

 does not seem to me fortunate ; it brings together such divergent types as Agassizia and Moira, aud 

 again Nacospatangus and Linopneustes. 



