600 Mr. H. L. Clark on the 



parts, a numeral and a participle, might be construed as an 

 indication that the full names (Echinodiscus quinquies 

 perforatus or 5 perforatus and E. sexies perforatus or 6 per- 

 foratus) are not binomial, and this would clear the way for 

 Gmelin's names ; but this seems to me such an unworthy- 

 quibble, I cannot bring myself to adopt it. 



Other genera which have been suggested at different times 

 for Recent clypeastroids seem to me to lack sufficient reason 

 for being. Thus the genera Diplothecanthus and Plesianthus, 

 Duncan, are due to the recognition of the wrong type for 

 Clypeaster and the laying of too much stress on the internal 

 structure of C. rosaceus. Mellitella is based on a remarkable 

 misconception by Duncan of the chai-acter of its type species, 

 Mellita stokes'u (Agass.). He states that the lunules remain 

 open as marginal slits. It is possible that he drew this con- 

 clusion from the figure given by A. Agassiz in the ' Revision ' ; 

 but he would have avoided error had he read the description 

 given in that work, for Agassiz distinctly says that the 

 iunules may be completely closed, as in other species of 

 Mellita. I may add here that I think there is no longer any 

 good reason for doubting that stokesiiis simply the young of 

 Eucope micropora ; hence Mellitella becomes a synonym of 

 Eucope. The genus Moulinia — or Moulinsia as emended by 

 Duncan, — established by Agassiz in 1841 for a little clype- 

 astroid from Martinique, is maintained by Duncan, 1885, 

 although Liitken and A. Agassiz considered its type to be a 

 young Eucope. A re-examination of the available evidence 

 has satisfied me that Liitken and A. Agassiz were right, and 

 I have therefore discarded the name. 



The more one considers the various characters by which 

 the families and genera of the clypeastroids are to be distin- 

 guished, the clearer it becomes that the position of the 

 auricles and their relation to each other is of very great 

 importance, although little weight has been attached to it 

 hitherto. The condition of theactiual ambulacral furrows is 

 also an important character, and fortunately is easily 

 observed. The arrangement and relative size of the inter- 

 ambulacral plates are characters usually difficult to make out 

 in adults, and as they are almost certainly correlated with 

 the shape of the test, too much stress should not be laid on 

 them. It is hard to decide how much weight may properly 

 be given to the arrangement of the internal calcareous 

 supports. It is hard to believe that it is of any great signifi- 

 cance, and it seems almost certain that the differences are, 

 in part at least, due to age. The distinction between 



