IN THE MOEPHOLOGT OF THE CTSTIDEA. 39 



point the Ordovician Bothriocidaris Pahleni, which has a single 

 ring of ten plates enclosing the anal system, he identified five of 

 these as the genitals and five as the oculars. He then continued : — 



" Wir konneu daraus mit Sicherheit schliessen class bei deu uralten Gruud- 

 formen der Seeigel die Tlieile aus welchen sich die Genital- imd Augentafelchen 

 der spiltei-en Typen entwiokelt babeii, nicht sclion zii zwei f 'imfzlililigeu, sondern zii 

 eineni eiuzigen, aus gleiclivverthigeii Stilcken bestehenden zehnhzahligen Kvanze 

 angeordnet waren. Damit ist die wichtigste Frage in der ganzeu Morphologie 

 der fossilen Seeigel gelost, oder die richtige Deutung evgibt sicb wenigstens von 

 diesem Standpunkte aus ziemlicli eiufacb von selbst, und wir werden sehen 

 dass dieses Ergebniss filr das Verstiindniss des ganzen Stammes der Echinoder- 

 men von grundlegeuder BedeuLung ist." (P. 364) 



Neumayr made use of these statements later on in the book 

 (p. 368) as an argument against the identification of the ocular 

 and genital plates of an Urchin with the radial and interradial 

 plates developed in two rings round the apical pole in other 

 Echinoderms, saying that the condition of Bothriocidaris shows 

 the impossibility of the dicyclic arrangement being the primary one. 



Neumayr's position thus depends on two fundamental as- 

 sumptions : — 



1. Grenital and ocular plates are present in Bothriocidaris 

 Palileni and are arranged in a single ring, not in two con- 

 centric rings, as in later forms. 



2. Because Bothriocidaris Pahleni is the oldest Ivnown 

 Urchin, therefore we are entitled to regard the structure 

 of its apical system as the primitive one for Urchins, and 

 to extend this view to the other Echinoderms. 



But was Neumayr right in asserting the presence of genital 

 and ocular plates in B. Pahleni ? Schmidt *, in describing the 

 genus, said expressly " Von G-enital- und Ocellarplatten keine 

 Spur;" and neither Loven, Agassiz, nor Zittel make any refer- 

 ence to their presence in this type, though Duncan t adopted 

 ISTeumayr's views. It may be that the five large plates at the 

 ends of the ambulacra are the oculars. But is it so certain that 

 the smaller plates alternating with them are the genitals ? JN'eu- 

 mayr took this for granted, though none of his predecessors had 

 ever suggested it, and he did not offer a single argument in support 

 of his opinion. Schmidt considered them as the uppermost plates 



* Mem. Acad. Imp. Sci. St. Petersb. 1874, tome xxi. IVo. 11, p. 38. 

 ■]■ " A Eevision of the Genera and Great Groups of the Echinoidea," Journ. 

 Linn. Soc, Zool. 1889, vol. xxiii. p. 8. 



