266 THE VOYAGE OF H.M.S. CHALLENGER. 



In each of these four species the disk is strongly plated, just as it is in the Basicurva-, 

 Spinifera-, and Granu /{/era-groups (PI. IX. fig. 2). But in all these three latter types 

 the pinnule -ambulacra have a well-defined skeleton and the lower parts of the rays are 

 flattened laterally ; whereas in Antedon elegans and its three allies, which we may 

 conveniently call the Elegans-gxowp, these characters are absent, the plating of the 

 perisome being confined to the disk. This seems to be a constant peculiarity of the 

 multibrachiate species of Antedon which have a syzygy between the two outer radials ; 

 and I have not seen any species possessing a plated disk, but no ambulacral skeleton on 

 the pinnules, which has articulated radials. 



The Comatula tessellata, Miiller, 1 seems, however, to be of this character. It has 

 ten arms with forty-five cirrus-joints, the later ones spiny, and was described as having 

 the " Haut der Scheibe mit kleinen Knochenplattchen bedeckt." Midler's type is (or 

 was) in the museum at Bamberg, but I have never been able to get a sight of it, and it 

 is the only one of all the described species of Antedon (if indeed it be an Antedon) 

 which I have not personally examined. It may of course be an Actinometra, though the 

 great number of its cirrus-joints rather precludes this supposition ; and there is also a 

 possibility that its two outer radials may be united by syzygy, though Miiller said 

 nothing to that effect. But its true position must remain uncertain for the present ; 

 and I would simply draw attention to the fact that the mode of union of the two 

 outer radials must be carefully examined when an attempt is made to determine the 

 systematic position of a multibrachiate Antedon with a plated disk ; for the probabibty 

 is that it belongs to Series I. 



Genus 5. Actinometra, Miiller, 1841 ; emend. P. H. Carpenter, 1887. 



1758. Asterias, Linnseus (jiars), Systema Naturre, 10th ed., Holmire, 1758, t. ii. p. 663. 



1783. Asterias, Retzius (pars), K. Svensk. Vetensk. Akad. Handl., Ar 1783, t. iv. p. 241. 



1805. Asterias, Retzius (pars), Dissertatio, sistens Species Cognitas Asteriaruru, Lunda3, 1805, p. 34. 



1816. Comatula, Lamarck (pars), Histoire Naturelle des Aniinaux sans Vertebres, Paris, 1816, t. ii. p. 530. 



1830. Comatula (Astrocoma), de Blainville (pars), Diet. d. Sci. Nat., 1830, t. lx. p. 229. 



1830. Alecto, Cuvier, Regne Animal, Paris, 1830, t. iii. p. 228. 



1834. Comatula (Astrocoma), de Blainville (pars), Manuel dActinologie, Paris, 1834, p. 248. 



1835. Comatula, Agassiz (jiars), Mem. de la Soc. d. Sci. Nat. de Neucbatel, 1835, t. i. p. 193. 

 1835. Comaster, Agassiz, Ibid., p. 193. 



1840. Comatula, Miiller (pars), Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1840, p. 91. 



1841. Actinometra, Miiller, Ibid., 1841, p. 180. 

 1841. Alecto, Miiller (pars), Ibid., 1841, p. 182. 



1843. Alerto, Miiller (pars), Abhandl. d. k. Akad. d. Wiss. Berlin, Jahrg. 1841 [1843], p. 203. 



1843. Actinometra, Miiller, Ibid., p. 226. 



1843. Alecto, Miiller (liars), Archiv f. Naturgesch., 1843, Jahrg. ix. Bd. i. p. 131. 



1843. Actinometra, Miiller, Ibid., p. 132. 



1843. Asterias, Miiller, Ibid., p. 133. 



1 Abhandl. d. h. Alcad. d. IFiss. Berlin, Jahrg. 1847 [1849], p. 251. 



