REPORT ON THE ECHINOIDEA MORTENSEN 305 



In the interambulacra the areoles are fairly deep and well sepa- 

 rated, at most the two proximal ones being confluent ; those on the 

 oral side are slightly transverse-oval. The uppermost areole is rudi- 

 mentary and without a primary spine, as is usual in stereocidarids; 

 but the areole and its tubercle are not so very small. The scrobic- 

 ular ring is very regular, rather conspicuous, but not raised, the 

 tubercles being more than twice as large as the marginal ambulacral 

 ones, and almost contiguous; outside the scrobicular ring the plates 

 are covered with small miliary tubercles of uniform size, which leave 

 just an indication of a 

 naked, but not sunken, 

 vertical median line. 

 There is an indication 

 of fine horizontal 

 transverse furrows, 

 especially on the oral 

 side. The median in- 

 terambulacral area is 

 scarcely half as broad 

 as an areole. 



The apical system is 



nearly half the hori- Fig. 22— Part of apical system of Stereocidaris sceptrifer- 



. * j- . rru OIDES, DODERLEIN, VAR. LAMELLATA, NEW VARIETY. X6 



zontal diameter. 1 he 



oculars are all widely exsert, small, with the inner edge forming 

 almost a half circle. Both genitals and oculars are rather elevated, 

 and are covered, not very closely, with tubercles of uniform size, 

 leaving a rather broad edge bare. The genital pores are near the 

 outer edge (fig. 22). The madreporite is not enlarged. Theperi- 

 proct is small, with rather few periproctal plates. The peristome is 

 flat, distinctly smaller than the apical system; there are 8 ambu- 

 lacral plates in a series, the ambulacra joining each other at the mouth 

 edge. The interradial plates are small, arranged in a fairly regular 

 double series of 4 or 5 plates in each series. 



The primary spines are conspicuously swollen at the base, thence 

 tapering gradually toward the tip, which is rather conspicuously 

 widened, with a central depression. The upper primaries are about 

 twice as long as the horizontal diameter; they diminish in length very 

 rapidly toward the oral side. In the basal part the larger upper pri- 

 maries are provided with about 12 prominent closely serrate narrow 

 ridges, which give the spine a lamellate appearance. In the outer 

 half these ridges become quite low, rising again at the expanded tip. 

 The surface of the spine between and on the sides of the ridges is 

 covered with a close coating of fine anastomosing hairs. The ridges 

 begin about 2 mm. above the collar, which is very low, scarcely 1 

 mm. high, and very inconspicuous, as is the milled ring. The portion 



