130 PROF. p. M. dunca.n's revision oe the 



are larger than those of the ambulacra, and all are largest 

 actinally. 



Fossil. Middle or Upper Tertiary : Patagonia, S. America. 



The genus Toxopneustes, Agassiz, 1841, is unsatisfactory ; and 

 in order to clear away some diiferences of ox^inion regarding 

 its value, it is necessary to revert to the diagnosis given in 

 the Preface to livi% 4 of ' Monogr. d'Ech. viv. et foss.' p. ix: — 

 "Le genre Toxopneustes a des ambulacres formes de series 

 arquees de doubles pores, convergeaat vers le milieu des aires et 

 separees par des rangees paralleles de petites pores. Chaque 

 serie arquee se compose de six a neuf paires de pores. Vers la 

 bouche il y en a moins ; mais elles sont plus rapprochees. Les 

 tubercules des series principales sont assez grands. L'ouverture 

 inferieure du test offre dix echancrures peu profondes. Je prends 

 pour type de ce genre VEcMnus tuherculatus ; j'eu conuai quelques 

 especes inedites." 



The genus had been simply named in livr. 2, p. 7, of the 

 same work during the same year ; and Echinus pileolus, Lmk., 

 was then decided to be the type. 



It is evident that Agassiz meant that the genus should in- 

 clude polypores ; and the word "pores," at the close of the 

 first sentence of the definition given above, should be "tuber- 

 cules." The genus thus covered the same ground as Strongylo- 

 centrotus, Brandt, 1885. 



The reason why Echinus pileolus was not made the type, when 

 the genus was finally diagnosed by Agassiz is tolerably evident ; 

 for it is not a polypore, and is more closely allied to a Tripneustes 

 than to Echinus tuherculatus. 



On reference to A. Agassiz's ' Revision,' p. 167, the synonymy 

 of the genus can be seen ; and it will be noticed that no less than 

 six genera have been founded which cover the same ground. 

 Toxopneustes did not reappear until the date of the ' Eevision,' 

 and four sjDecies of it are admitted by the distinguished author — 

 T. maculatus, T. pileolus, T. semituherculatus, T. variegatus. But 

 it is a matter of fact that not one of these species has the generic 

 characters defined by the elder Agassiz in the ' Monographie.' 



There is therefore no such genus as Toxopneustes, Agassiz ; he 

 merely gave a name, and his diagnosis did not distinguish his 

 two types. In the ' Eevision ' of A. Agassiz, ]). 297, there is a 

 generic definition of Toxopneustes which differs very materially 



