HOLOPNEUSTES PYCXOTYLUS. 335 



ous scattered pore-pairs. Most of the ambulacral plates carry primary tubercles, 

 but in scarcely a third of them is this tubercle adjoining the poriferous area. 

 The plates are very unequally developed and some are much higher than others. 

 The areolae of the primary tubercles nearly or quite equal the height of the plates. 

 Eadi plate has about four secondary tubercles, at least one of which is nearly 

 or quite as large as the primary, and two are usually very small and are located 

 in the poriferous area. In the type, miliary tubercles appear to be wanting but 

 in other specimens, they are fairly numerous. Each interambulacral plate at 

 the ambitus carries a primary and 5-8 secondaries. The primaries are a little 

 nearer the outer than the inner end of the plates and form a regular vertical 

 series. In typical cases, with low plates, this series is crowded, the areolae 

 occupying the full height of the plates, but in the type and some other specimens 

 the plates are higher and the tubercles more separated. One or more of the 

 secondaries is nearly or quite as large as the primary and sometimes the row of 

 primaries is thus made to appear double for part of its length. The madreporic 

 genital is conspicuously larger than the others. The oculars are small and fully 

 exsert. Both genitals and oculars are well covered with tubercles, but the 

 numerous periproctal plates carry none. The actinostomal membrane is very 

 thin and perfectly naked. The buccal plates are very small and placed quite 

 near the mouth. 



The primary spines of the type are about 4 mm. long, rather stout and bluntly 

 pointed. Most of them taper slightly to the tip, but many are distinctly swollen 

 there. The secondaries are much more slender than the primaries but some are 

 about as long. Many of them are swollen at the tip. Pedicellariae are very 

 numerous but excepting some of the ophicephalous, which have valves over half 

 a millimeter long, they are all very small. Otherwise neither they nor the 

 spicules afford any characters of interest. 



The type is uniformly dirty cream color, spines and all, but most of the other 

 specimens are gray with more or less of a purple, or a red, or a yellow tinge, and 

 their spines show the same shades to a greater or less degree. 



Most of the specimens of pycnotylus have been received from Port Jackson, 

 New South Wales, labelled '^ Amhlypneustes ovum.'' One label further says: 

 "Coastal beaches outside; after gales only," but other specimens do not have 

 this limiting phrase on the label. 



