ECHINODBRMA. 9 



margin very sharp, the inner actinal ambulacrals with spines, the oral angle provided 

 with a large spine. While the specific characters would appear to be that the longer 

 radius is more than twice as long as the shorter radius, the marginal plates are very 

 numerous, and the innermost ambulacral spine is spatulate and fluted at its free end. 



The smallest specimen has not quite acquired the generic characters of the larger ; 

 the abactinal integument is not so thick as to altogether hide the superficial granules, 

 and the granules on the actinal interambulacra have not developed into spines, so that 

 there is no marked difi'erence between the outer and the inner parts of these areas. 



Pentagonaster incertus. 



The single small specimen, is, I think, an ally of the Australian species of Penta- 

 gonaster (sens, lat.), but the arms are proportionately longer than they generally are 

 in this genus ; it is, possibly, an immature specimen in which R would gradually 

 increase in proportion to r. If it should prove to be an adult, its proportions may be 

 compared to those of P. duebeni and P. gunni ; it is, however, to be distinguished by 

 the fact that there are no large plates on the actinal inter-radial areas, the plates being 

 of the character of, and a little larger than, the small squarish granular plates which 

 bound the marginals; these last number about 12/14 for the side of each arm, and 

 are completed by a large terminal ; there are two rows of well-developed spines at the 

 sides of the ambulacra ; those of the inner row are nearly twice as long and as 

 numerous as the outer. I propose to call this form Pentagonaster incertus ; it was 

 taken at 96-120 fms., in MacMurdo Bay. 



Leptoptychaster kbrguelenensis. 



Leptoptychaster kerguehnensis, E. A. Smith, Phil. Trans. 168 (1879), p. 278, pi. xvii. 2 ; Sladen, Chall. 



Eep. Ast. (1889), p. 184; Bell, Mar. Invert. S. Africa ill. (1905) p. 242. 

 Leptoptychaster antarcticus, Sladen, op. cit. p. 190. 



I must own to some temerity in associating a specimen in which 7? = 212 and 

 r = 58 with a species whose type had i2 = 38 and r = 12*5, and a representative 

 of which, hardly much larger, was found to be bearing young; but even the most 

 recent writers on Echinoderms have not yet promulgated the doctrine that difierence 

 in size is a specific character, though I am not quite sure that in practice they do 

 not sometimes act as though they had. However, one has only to get a clear idea 

 of the essential characters of this genus to feel sure that one has it here ; as to specific 

 characters, it is first to be said that most of the L. kerguehnensis material is badly 

 preserved, while the condition of L. antarcticus is particularly good. Though the 

 differences between the two species appear, from Mr. Sladen's lengthy description, to 

 be considerable, it will, I think, be found on examination of the specimens preserved 

 in the Museum, that L. antarcticus is but the expression of some early stages of 

 L. kerguehnensis. It will be remembered that both " species " come from closely 

 adjacent localities. At any rate, we now know that the specimens of L. antarcticus 



