Published online by Cambridge University Press: 01 May 2009
In two previous papers in this Magazine (Hawkins, 1910 and 1911) I have dealt with some features in the comparative anatomy of the ambulacral and interambulacral areas of the Holectypoida. The only other structure of the test for a comparative study of which sufficient material is available is the apical system. The present paper deals with this structure. I intend to summarize the results of my researches in a scheme for the classification and evolution of the group in a paper already partly prepared.
1 This name is systematically indefensible, being synonymous with Agassiz's Pygaster whose type is P. semisulcatus. I use it in inverted commas here to avoid systematic discussions in a morphological paper.