REPORT ON THE CRINOIDEA. 3 



subsequently added by Bohlsche 1 after the type had been accorded generic rank by 

 Dujardin and Hupe, 2 who improved considerably upon Midler's definition of it. The 

 German zoologist had not considered the position of the mouth as a point of any 

 systematic importance ; but he referred to Alecto both species like Antedon rosacea and 

 Antedon eschrichti, which have five symmetrically distributed ambulacra radiating from 

 a central mouth, and also species with an equally symmetrical grouping of the ambulacra, 

 but with an excentric mouth. Dujardin and Hupe, however, took no account of the 

 number of ambulacra diverging from the peristome, to which Mliller attached so much 

 importance ; but they pointed out that the distinctive character of Actinometra rather lay 

 in the excentric position of the mouth, which determined the course of the ambulacra 

 round the margin of the disk, instead of towards its centre. Nevertheless, they did 

 not transfer to Actinometra the various species of Alecto described by Muller with an 

 excentric mouth and symmetrically grouped ambulacra ; so that they did not make any 

 real addition to the genus, although they recognised its characters better than Muller 

 had previously done. Single species were subsequently added to it by various writers, 

 but it was never properly defined. 



Having assigned a generic value to Actinometra, Dujardin and Hupe" did the same 

 for Midler's type Alecto, for which, however, they preferred Lamarck's name Comatula. 

 But three years later Mr. Norman replaced this by Antedon, a name which was originally 

 proposed earlier than either Alecto or Comatula; and at the same time he restricted it 

 to those species only in which the mouth is central or subcentral and the anus lateral. 

 Very nearly all subsequent writers have accepted this definition of Antedon ; but no 

 attempt was ever made to modify the Mullerian descriptions of Comatula in accordance 

 with it. 



Towards the end of 1875, ten years after the publication of Mr. Norman's precise 

 definition of Antedon, I had the opportunity of studying a large collection of tropical 

 Comatulse which had been obtained by Professor Semper in the Philippine Islands ; and 

 it soon became evident that the number of ambulacra diverging from the peristome is so 

 variable as to be useless for the purposes of generic discrimination. At the same time 

 other characters seemed to be correlated with the central or excentric positions of the 

 mouth respectively ; and I came to the conclusion that the real distinction between 

 Antedon and Actinometra respectively is based upon this feature of their organisation, 

 the number of groove trunks connected with the peristome being a character of very 

 minor importance. 8 I soon learnt that Professor Liitken had held this opinion for some 

 time past; and he also pointed out to me certain characters of the oral pinnules which are 

 always associated with the excentric position of the mouth. Since that time I have 



1 Ueber Actinometra Bennettii unci eine neue Comatula Art (Autedou Dubenii), Archiv f. Naturgesch., 

 1866, Jahrg. xxxii. Bd. i. p. 90. 



2 Op. cit., p. 208. 



3 Trans. Linn. Soc. Lond. (Zool.), 1879, ser. 2, vol. ii. pp. 17, 18. 



