50 BULLETIN 16, UNITED STATES NATIONAL MUSEUM. 



wlion ilry) surmount a very low convex elevation or tabuluni. Well-defmcd fas- 

 ciolar fhiumols separate these tabula. 



Adaiubulacral plates about as wide as long, with a sHghtly rounded, angular 

 furrow margin, the angularity being more pronounced m vicinity of mouth plates. 

 Armature consists of (1) a furrow series of four (sometimes three) terete or slightly 

 liattened bluntly pointed tapering spinules about as long as plate and graduated in 

 length orad, the longest s])ine being on aboral end of plate; or the spinules may be 

 disposed like rays of fan and graduated hi length toward either end of series. (2) 

 On actinal surface are about three longitudinal series of smaller spinelets, decreasing 

 in length toward outer edge of plate where the spinelets are like those of actinal 

 uitermediate plates. Four spinelets commonly occur in the inner actinal series 

 and about three to five in each of the outer; or the two latter series may be wanting, 

 the spinelets, instead, forming an irregular group, especially on outer part of ray 

 where tliere are frequently upward to sixteen or twenty actinal spinelets. 



Mouth plates narrow, rather prominent actinally, the free margins of the 

 combined plates forming a salient angle into actinostome; free margin of each 

 plate slightly angular near inner end and longer than the margin adjacent to first 

 adambulacral. Armature consists of a furrow series of about six or seven tapering 

 spinules decreasing in length from the inner enlarged tooth, outward, and thence 

 continued along margin adjacent to first adambulacral in about nine much smaller 

 sphielets similar to those of actinal uitermediate plates. A superficial series of 

 similar spinelets follows margin of median suture, increasing in size toward umer 

 angle of jilate, and an incomplete more or less irregular series often, but not always, 

 occurs between marginal and superficial series. There is more or less variation in 

 the details of dental armature. The exposed, outer, slightly convex surface of the 

 combined plates has the appearance of being covered with a bristling armature of 

 short papilliform sphielets, ver}' similar to those on adjacent actinal intermediate 

 plates. 



Madreporic body rather large, about midway between center and extreme edge 

 of disk. Striations coarse, centrifugal, very irregular; madreporic body sometimes 

 nearly liidden by five or six large paxillse. 



Superambulacral plates present, though small. Absent from the first ambu- 

 lacral plates, and from the distal six or seven, wliich are much reduced and crowded 

 against the adjacent inferomarginals. Gonads forming a tuft of tubules on either 

 side of the interradial septum, five or six tubules (two or tlireo times dichotomously 

 divided) to each tuft. The gonads do not consist of a series of tufts extending 

 along the ray as in Dipsacaster. A Pohan vesicle in each interradius. Interradial 

 septa uncalcified. 



Variations. — The siiecimens assembled under tliis form present a very con- 

 siderable amount of variation, and when the extremes are placed side by side it is 

 hard to believe that there are not two valid species. But there is such a bewildering 

 number of more or less perfect intermediate stages that one is forced to range them 

 all under one head. 



The most important variations occurring in this species are in respect to 

 dimensions and the size of the marginal plates. Some examples have a more stellate 



