REPORT ON THE ASTEROIDEA. 285 



is situated nearer the margin than the centre of the disk, at the top of the lateral wall in the 

 iuterbrachial arc, and is surrounded by the spinelets borne on the adjacent abactinal plates. 



No pcdiccllarise of any kind are present. 



The ambulacral tube-feet have large fleshy disks. 



Colour in alcohol, an ashy grey. 



Locality. — Station 156. In the neighbourhood of the pack ice, near the Antarctic 

 Circle. February 26, 1874. Lat. 62° 26' 0" S. ; long. 95° 44' 0" E. Depth 1975 

 fathoms. Diatom ooze. Bottom temperature 32 - l° Fahr. ; surface temperature 3 7 "2° Fahr. 



Genus Gnathaster, n. gen. 



It is not without great reluctance that I have proposed a new generic name for the 

 present small group of species. I had hoped in the first instance to have limited the term 

 Astrogonium in such a way as to have served for their reception, since all the species 

 except the new ones have at various times been ranked in that genus. Unfortunately, 

 however, they do not comprise a single species referred by Miiller and Troschel to their 

 genus ; and on carefully studying the diagnosis given in the System der Asteriden 

 (p. 52) it will be seen that that diagnosis could in no way be amended so as to admit of 

 the reception of the forms now under consideration, without such a radical alteration as 

 would really take away from it the only characters upon which its original recognition 

 depended. 



On referring to the series of species grouped by Miiller and Troschel in the genus 

 Astrogonium, it will be apparent that all of them, excepting the form originally described 

 by Gray ' under the name of Pentagonaster pulchellus, are referrible to the older genera 

 Pentagonaster of Linck and Hippasteria of Gray. It is therefore to this form, Penta- 

 gonaster pulchellus, Gray, and its subsequently described allies, that the generic appella- 

 tion of Astrogonium should now be applied, if the name is retained at all. 



Perrier 2 has recently expressed the opinion that this type (Pentagonaster pulchellus, 

 Gray), together with a small assemblage of allied species, is worthy of independent generic 

 recognition. This view appears to me just, and based on the presence of characters the 

 morphological significance of which had hitherto been overlooked. As a generic name 

 for this group, Perrier has restored that of Stephanaster of Ayres, 3 on the ground that 

 Stephanaster elegans, Ayres, is synonymous with Pentagonaster pulchellus, Gray, or in 

 other words, that the form described by Gray in 1840, under the name of Pentagonaster 

 pulchellus, was redescribed by Ayres in 1851 under the name of Stephanaster elegans, on 

 the supposition that it was a genus and species new to science. 



With this selection of a name for the group in question I am unable to agree, for in 



1 Ann. and Mag. Nat. Hist., 1840, vol. vi. p. 280. 



2 Ann. Sci. Nat. (Zool.), 1885, t. xix., Art. No. 8, p. 30. 



3 Froc. Boston Soc. Nat. Hist., 1851, vol. iv. p. 118. 



