502 PROF. F. J. BELL ON THE GENUS ASTERIAS. [May 3, 



iii. POLYACANTHIDA. 



panopla. 



The number of species in the first two groups of the Pentactinida 

 is still so large that we must now attempt to find some means by 

 which they may be still further subdivided. 



Among a certain number of forms we find a special modification 

 of some of the dorsal spines, which come to form an encircling 

 fringe around the madreporic plate. In some species these spines 

 are obvious enough ; but I know of no author except Prof. Verrill 

 who has directed any attention to them\ or attached any impor- 

 tance to their presence. As, however, I will show in detail further 

 on, I cannot give in my adhesion to the validity of the genus Lep- 

 tasterias, even when the proposition comes from so deservedly 

 honoured and distinguished a naturalist. I doubt, in fine, whether 

 they can be used as any thing more than a convenient separation- 

 character in a genus where specific characters are so rare. 



The species, then, which are provided with a circlet of spines round 

 their madreporic plate may be distinguished as the Echinoplacida ; 

 such among the Diplacanthid Pentactinida are : — 



A.fulva (with 18 spines). 



A. germaini (with spines indistinct). 



A. lurida (with 12 spines). 



A. nuda (with spines irregularly distributed). 



A. obtusispinosa (with 12 spines). 



A. sinusoida (with spines irregularly distributed). 



A. spectabilis (with 18 spines). 



It is curious to observe that, as yet, the echinoplacid condition has 

 not been noted as obtaining among the Monacanthid Pentactinida ; 

 among the Polyactinida the echinoplacid condition seems only to 

 have been observed in the diplacanthid monoplacid form acervata, 

 where there are said to be 13 spines around the madreporic plate. 



In a description of the species A. brandti, which I lately communi- 

 cated to the Society^, I have directed attention to the mode of arrange- 

 ment of the greater number of the intermediate spines on special local 

 modifications of the integument, which may be known as special 

 plates. This arrangement should be familiar enough ; for it is to be 

 found in A. te?iuispina, and is represented in the figure of that species 

 given by Miiller and Troschel (' System der Aster.' pi. i. fig. 1 b). 

 The forms in which the spines thus rise from special plates may be 

 distinguished as autacanthid. 



In such a group we should find : — the Polyactinid meridionalis, 

 perrieri, tenuispina, and (probably) scabra ; and the Pentactinid 

 Diplacanthid brandti and neglecta. 



When the spines retain the simpler disposition which is seen in 

 A. rubens and most of the better known forms, we may speak of the 

 arrangement as being typacanthid. 



' Of course such a naturalist as Pliilippi does not fail to note their presence. 

 ^ P. Z. S. 1881, p. 91. 



