PRIONECHINUS RUBER. 305 



men also, the spines are 5 mm. long, but the number of interambulacral and 

 ambulacral plates in each column is 9. The sculpturing of the test is almost 

 wholly wanting; it is simply indicated by slight depressions on the sutures and 

 granular swellings among the tubercles. The genital plates (PI. 100, fig. 6) are 

 large, subequal, and rather closely covered with small tubercles; the pores are 

 quite distinct near the centre of each plate. The madreporic pores are remark- 

 ably few (10 -12) and consequently the madreporite is not easily detected. The 

 oculars are of moderate size, well covered with small tubercles and are all fully 

 excluded from the periproct. The latter is larger than a genital plate and is 

 covered by about a dozen plates (or more) among which the suranal can be 

 distinguished by its size, though several other plates are nearly as large. The 

 ambulacra are very broad but do not equal the interambulacra at ambitus. 

 The poriferous areas are very narrow, the small pore-pairs being arranged in 

 nearly vertical arcs of three. The primary tubercles, of which there is one on 

 each coronal plate, form conspicuous vertical series on each column of plates, 

 those of the ambulacra about as large as the others. Secondary tubercles are 

 not numerous, usually two or three on each ambulacral plate and four to seven 

 on the interambulacral. There are also rather numerous granular elevations 

 which may be miliary tubercles, but their outlines are so indistinct that they may 

 not be tubercles at all. The actinostomal membrane (PL 100, fig. 5) is thin and 

 outside the circle of buccal plates is almost bare. The buccal plates are large, 

 each carries a tube-foot and they are nearly or quite in contact with each other, 

 thus forming a more or less complete closed ring, within which the membrane 

 is completely covered with small plates. The primary spines at ambitus are 

 about half as long as the test-diameter, while the abactinal ones are very much 

 smaller. The secondaries are short, stout, and somewhat club-shaped. 



The pedicellarise are not remarkable but resemble those of the other members 

 of the genus, particularly those of sagittiger and Chuni as photographed by Doder- 

 lein. The globiferous are common and have the valves .30 -.35 mm. long; it is 

 not uncommon to find a lateral tooth on each side, instead of on only the left 

 side as is usually the case. In the ophicephalous, the valves are about .30 -.35 mm. 

 long. The tridentate are fairly common, but of very variable size, the valves 

 ranging from .35 to .80 mm. In the small ones the valves are relatively much 

 wider than in the large ones, but even in the latter the valves are a little wider 

 than in sculptus. No triphyllous were found, nor were spicules or sphseridia 

 observed. 



In the smaller specimen the colors, are quite bright; the test is orange-red, 



