404 ARBACIA STELLATA. 



actinal part of the test there are four diagonal rows of nearly uniform-sized 

 tubercles. The ambulacral and interambulacral tubercles are of nearly the 

 same size on that part of the test, but the former decrease rapidly in size 

 above the ambitus, corresponding fully to the decrease of tbe primary inter- 

 ambulacral tubercles. The actinal cuts are broad, deeply cut, with prominent 



lips. 



Tbe abactinal part of tbe poriferous zone above the ambitus is very broad, 

 although the pores are not crowded laterally as in A. nigra. The nature of 

 the spines is very variable in this genus, and the spathiform character of the 



spines of the lower surface was only found to exist to an unusual extent 

 above the ambitus in the original specimens of Valenciennes. The actino- 

 stome is comparatively small, as in A. nigra. The auricles of the specimens 

 examined are barely connected. 



Dried specimens are light brown, with reddish tinge below, of a dark 

 ground-color of same shade in median interambulacral zone above ambitus. 



Test with a rounded outline uniformly arched, but less pentagonal than 

 A. pustulosa, though not often conical as in A. punctulata, and less depressed 

 than A. stellata. 



Chili; Prill. 



Arbacia stellata 



I Echinus strllntu* (Blainv.), 1825, Dirt. Sc. Nat O. 

 ! Arbacia stellata Gray, 1835. Tin,, /.mil. Soc. London. 



The facies of this species recalls strongly Arbacia punctulata, to which it is 

 extremely closely allied ; the proportion of the spines to the test, their mode 

 of distribution, and the general structure of tin- abactinal system, is nearly the 

 same. It differs from it in the greater breadth of the ambulacral zone, due to 

 the greater width of the poriferous zone; the ambulacral zone rising above 

 the level of test, giving to the outline a more or less pentagonal aspect. The 

 height of the coronal plates is greater, the size of the primary tubercles 

 larger; and in specimens thus far collected the bare median interambulacral 

 space remains quite marked, but not as distinctly prominent as in A. Du- 

 fresnii, the primary vertical rows of tubercles not extending much above the 

 ambitus. At the ambitus the ambulacral and interambulacral tubercles are 

 nearly of the same size. The part of tbe plate occupied by the miliary granu- 



