JAPANESE ASTEROIDEA. 487 



" LocaUfy. This species is found not imcommonly in about a fathom of 

 water on the shore of the lagoon off the east side of Singapore Island. 



" Distrilmtion. Indian Ocean, Eastern Ai'cliipelago, and N. Australia. 



" The systematic classification of the genus Pcrdaceros offers similar 

 difficulties to those found in the Echinoid Diadema ; in both cases we have 

 exceedingly variable groups of individuals in which the norm of the varia- 

 tions is different in different localities. The four ' species ' Pentaceros turri- 

 tm M. Sc T., P. h'ndcus M. & T., P. muricatus Gray, and P. alveolahis 

 Pereiee, which Professor Bell describes as ' apparently distinct,' are based 

 on characters which are admittedly subject to very great variation ; and while 

 Prof. IjELL instances the presence or absence of marginal spines as a charac- 

 ter by which 'we can always safely discriminate between 0. I'mcld ( = P 

 muricatv.s) and 0. nodosus { = P- turritus) ' {loc. cit. p. 59), at the same time 

 Dr. Martens had named two varieties of P. muricatus (var. mutica and var. 

 intermedia) in which the marginal spines completely fail : this of course is 

 entirely due to the fact that no two observers are agreed as to the best set 

 of characters to select for specific diagnoses, and in consequence a totally 

 different grouping of the same series of specimens would be resorted to by 

 different systematists. Whether it is advisable in such a case to unite all 

 the forms under one specific name, as has been suggested for the Pacific 

 Diademas hj Prof. LovÉN, I do not feel in the least competent to express an 

 opinion. 



" Specimens both with and without a centi-al apical tubercle occur at 

 Singa]X)re as elsewhere, and in the former case the apical tubercles may Ije 

 much longer and sharper than in the latter, in which they are usually 

 mamillifoi-m ; I do not know if individuals with the marginal spines deve- 

 loped occiu' in the locality. 



" Two specimens gave the following measurements : — 



" li (act. side) = 116 mm., r=46 ; arm-breadth = 5-4; no. of marg. plates 

 = 23 ; 9 lopliial tubercles, 3 or 4 inten-adials. 



"R (act. side) = 128 mm., r=52; arm-breadth = 58 ; no. of marg. plates 

 = 27 ; 7 or 8 lophial tubercles, 4 interradiais." 

 - 1'feffer simply mentions Pentaceros turritus Linck from Ternate [:0{), 



