486 HOLOPNEUSTES PURPURESCENS. 



the latter is characterized by the greater size of the inner pore, and the 

 distance separating the pores of a pair. The tubercles of both areas form 

 most regular horizontal rows, as many as ten tubercles of nearly uniform 

 size, diminishing gradually towards the median line, and forming regular 

 vertical lines towards the poriferous zone on each side of the median line in 

 specimens of 80 mm in diameter, and from one to three for the ambulacral 

 spaces, forming no distinct vertical rows. 



The test is thin, the poriferous zone being narrower than in the other 

 species of the genus. The color of the small specimens, measuring 35 mm in 

 diameter, is a beautiful light violet, with greenish median bands both in the 

 ambulacra and interambulacra and along the outer edge of the poriferous 

 zone. In the large specimens the test is of a uniformly yellowish-brown 

 color. 



Specimens of Holopneustes are not common in museums, so that, with the 

 exception of the variations observed in H. inilatus, it is difficult to know 

 how far the species of the genus vary. The variations observed in II. inila- 

 tus and II. purpurescens are limited mainly to the poriferous zone in the 

 young specimens, the three vertical rows of pores being at first quite distinct, 

 then the middle row becomes undulating, and finally, with the lateral spread- 

 ing the original arrangement is completely lost sight of. It may be that II. 

 purpurescens will prove to be nothing but II. porosissimus with a rather 

 narrower poriferous zone, the variations of the size of the pores recalling 

 similar differences noticed in Toxopneustes pileolus. Additional material is 

 needed to discriminate better the species of Holopneustes temporarily distin- 

 guished in the Museum Bulletin. 



New Holland. 



