GEJiTEEA AND GROUPS OP THE ECHINOIDEA. 5 



rarely anterior ; jaws and teeth present or absent. Periproct 

 either within the dorso-central system or in the posterior inter- 

 radium. 



I. Subclass FAL^EGSINOIDEA. 



The Palaeechinoidea have gradually become a great group 

 which is readily separable from all the other divisions of the 

 Echinoidea. The first careful descriptions of its genera and species 

 were given by McCoy in his " Description of the Carboniferous 

 Eossils of Ireland;" subsequently Baily, Meek and Worthen, Hall, 

 and J. Miiller added greatly to the knowledge of the anatomy 

 and taxonomy. In ' Les Etudes,' Sven Loven summarized the 

 information which had been obtained up to 1874 and mainly 

 followed McCoy's classification. About the same time A. Agassiz 

 gave some important notices of the Perischoechinidse, McCoy, 

 then the only group of Palaeechinoidea, in the ' Revision of the 

 Echini' (p. 644). In the course of his observations A. Agassiz 

 criticised the classifications of previous authors, and very pro- 

 perly drew especial attention to the discovery of J. Miiller 

 regarding the overlapping of the coronal plates of some genera, 

 and he compared this phenomenon with the imbrication of the 

 peristomial plates of Cidaris and of the coronal plates of 

 the Echinothuridae. It became evident that a new taxonomy 

 of the group was necessary, and Messrs. B,. Etheridge, Junr., and 

 W. Keeping contributed papers (1874-6) to the Geological Society 

 of London, in which the limits of the new classification were 

 fairly stated. 



Discoveries of some remarkable forms, such as Bothriocidaris, 

 Schmidt, 1874,T««recAim<s, Neumayr, 1881, and the reconsideration 

 of EcMiiocystites, Wy. Thomson, 1861, necessitated the intro- 

 duction of groups which could not be placed as Perischoechiaidae. 

 Zittel gave an admirable classification in his ' Palaeontologie,' 

 1876-80 ; and finally A. Agassiz introduced some pages in his 

 lieport on the ' Challenger ' Echini, 1881, which are full of most 

 valuable matter. He had the opportunity of studying the rare 

 species described by American palaeontologists, of which plates 

 and figures alone have been noticed by European geologists, and 

 he brought to bear on their consideration a vast amount of 

 knowledge about the recent Echini and especially of the Echion- 



