1884.] SPECIES OF OREASTER. 73 



to the tips of the spines. Madreporic plate rather small, not con- 

 spicuous. 



Colour (when dry) — lower surface reddish, upper reddish where 

 the granules are developed, with grey poriferous areas ; in some cases 

 the dried specimens are almost white, but this may be due to the 

 mode of drying. 



The above description has been drawn up from a set of five speci- 

 mens, which were collected at the same time and place (between tide- 

 marks, at the Mozambique, in May 1882) by Dr. Coppinger, H.M.S. 

 'Alert', and illustrate the exactness of the statement of Dr. von 

 Martens : — " Alle diese Variationeu kreuzen sich so sehr durchein- 

 ander, dass man darnach keiue irgendwie bestimmbaren Lokalvarie- 

 taten aufstellen kann" '. The variations are so marked that it seems 

 to be impossible to follow Dr. von Martens in establishing definite 

 " varieties." The exact state of the case is, I think, this. The 

 strength of the marginal and ventral plates, with their coarse granula- 

 tion, is sufficient for the safety of the Starfish ; the spines are additional 

 defences that are not constantly needed, and are developed more ac- 

 cording to the conditions of individual environment than in obedience 

 to the necessities of the species. They are organs which have begun 

 to disappear, and their importance to their possessor may be judged 

 of by the extent to which they vary in number and size on the 

 different arms of one and the same individual. The species stands 

 midway between O. alveolatus, in which inferomarginal spines are also 

 developed, and O. nodosus, in which there are no marginal spines at all. 



Hab. Indian Ocean (Mauritius, Timor). 



OrEASTER ALVEOLATUS. 



Pentaeeros alveolatus, Perrier, Rev. Stell. p. 243. 



At first sight this species has the most remarkable resemblance to 

 O. lincJci, but it is at once to be distinguished from it by the constant 

 possession of inferomarginal spines. 



R=2'7?'. Disk very higb, lophial line well marked; lophial 

 spines well developed ; apical very prominent. The arms diminish 

 but little in breadth from the proximal to the distal end. 



About 21 marginal plates ; at the angles the inferomarginals form 

 the sides, while the superomarginals are rather obscure, and these 

 inferomarginals are provided with rather short spines ; the supero- 

 marginals gradually become larger, and oust the inferior plates 

 from any share in forming the sides of the arms, while they develop 

 prominent spines ; towards the tip of the arm spines, or spinous 

 tubercles, reappear on the inferomarginal plates. 



Adambulacral spinulation diplacanthid ; five or six spines in the 

 inner row, not remarkably delicate ; those of the outer row pretty 

 stout and arranged by twos or threes. A spiniform pedicellaria is 

 ' Arch, fiir Naturg. xxxii. 1866, p. 79. 



