504 ON A COLLECTION OP ECHINODERMATA FROM AUSTRALIA, 



Though Mi*. Tenison- Woods would appeal' to have an extra- 

 ordinary familiarity and acquaintance with Echinoidea, second 

 possibly only to that of Prof. Alex. Agassiz, with whose description 

 and views his own so often and so curiously agree, yet he is, I 

 think, mistaken in imagining that there is any mysterious 

 constancy in the number of the primary tubercles ; when there are 

 but few tubercles, that is where the primary plates are large we 

 easily count, and sharply note the number of such bosses ; but with 

 an increase in the size of the test, there must come some increase 

 in the number of the plates. In other words, because the largest 

 specimen (75 mm.* in diameter) known to-day has only 6 tubercles, 

 it by no means follows that a specimen of the same species, found 

 to-morrow with a diameter of 100 mm. with not have more. 



At this moment a specimen of Phyllacanthus imperialis lying 

 before me has a diameter of 80mm., and seven primary tubercles 

 in a vertical row. 



A specimen of 60 mm. in diameter may therefore well have only 

 seven primary tubercles, and yet belong to the same species as the 

 test with 100 mm. for diameter and eight primary tubercles. 



I have followed Prof. Agassiz and Mr. Tenison-Woods in the 

 term Phyllacanthus, but I have to say that I have done this rather 

 because I have here wished to keep apart from all disputed 

 questions, and not because I do not myself recognise a force 

 in de Loriol's plea in favour of Rhabdocidaris. (See Palseento- 

 graphica. Vol. XXX. pt. II., p. 6. 



" Phyllacanthus. Sp. Nov. (unique.") — A specimen bearing the 

 above remark cannot be passed over without notice. It will 

 exhibit to the visitors of the Australian Museum an example of 

 what may well be called symbiosis, for the well developed 

 Polyzoan colonies must afford protection to the species, and the 

 small parasitic Balani gain all the food they want in the currents 

 that stream round so much larger an organism. 



*Strangely enough the American and the Australian Naturalist fix on just 

 the same number of mm. 



