. Bulletin - United States National Museum. Science. 284 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM tubercle is rather small with the boss low; there is no trace of crenulation, but there are more or less distinct radiating furrows in the areole. The scrobicular ring of tubercles is rather inconspicuous, the tubercles being only a little larger than the marginal ambula- cral tubercles. Outside the scrobicular ring the plate is covered by miliary tubercles of uniform size, leaving a rather conspicuous naked sunken median line, with a fairly distinct groove at the inner end of the horizon
. Bulletin - United States National Museum. Science. 284 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM tubercle is rather small with the boss low; there is no trace of crenulation, but there are more or less distinct radiating furrows in the areole. The scrobicular ring of tubercles is rather inconspicuous, the tubercles being only a little larger than the marginal ambula- cral tubercles. Outside the scrobicular ring the plate is covered by miliary tubercles of uniform size, leaving a rather conspicuous naked sunken median line, with a fairly distinct groove at the inner end of the horizontal sutures. On the adradial side of the scrobicular ring there are also some miliary tubercles. The median area is very narrow, only about one-third the width of an areole. The apical system is rather unusually large, more than half the hori- zontal diameter and somewhat elevated. The ocular plates are all widely exsert; the madreporite is not enlarged. The periproct is rather small, with a moderate number of small periproctal plates. The whole apical system is closely covered with small tubercles of uniform size, leaving a narrow bare zone along the inner edge of the genital plates. The genital pores are large and are situated close to the outer edge of the plates (fig. 18). The peristome is only about half the size of the apical system and is distinctly sunken. Fig. 18.—Part of apical system of Psilocidakis echinulata, new There are onlv 3 Of 4 SPECIES. X6 till- ambulacra! plates in a series; the ambulacra join at the mouth edge. The interradial areas are very small with only 1 or 2 small plates each. The primary spines are very long, four or five times the diameter of the test; even the longest spine in the best specimen has the point broken; in the second specimen not one of the ambital spines is complete. These spines are straight, very slender, cylindrical, taper- ing very gently to the (apparently) fine point. They are covered with small spinules which are erect or on
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