283 
The general outline varies rather considerably, some (mainly 
the larger) specimens being almost regularly pentagonal, others 
having the interradial margins very concave and the arms fairly 
prominent. A few measurements will illustrate this: 
R—54 mm, r—38 mm. R=l,4 r. 
R—42 mm, r—22 mm. R=l,9 r. 
R—26 mm, r—17 mm. R=^l,5 r. 
R—18 mm, r—10 mm. R=l,8 r. 
The disk is covered with rounded plates, each surrounded by 
a circle of fine grains. Seen from the inside the plates are star¬ 
shaped, the pores of the papulæ lying in groups between the rays 
of these plates. The plates are more or less elevated, especially 
a regular median series along each ray and a rosette of 5 —6 
plates in the middle, round a central plate are generally distinctly 
elevated, knobshaped. The plates of the side areas of the rays 
may be more or less distinctly arranged in series parallel to the 
median series. — The madreporite is large and conspicuous, situated 
nearer the centre of the disk than the edge, and is often surrounded 
by three more prominent plates; but this is by no means constant, 
the surrounding plates being sometimes 4 or 5. The plates of the 
disk show a peculiar structure, being mottled with numerous small 
clear spots of a more glassy structure, different from the rest of 
the plate; probably these clear spots correspond to the “crystal 
bodies” in the plates of Goniodiscus o. a. (Cf. Doderlein. Ober 
Krystallkorper bei Seesternen. Jen. Denkschr. VIII. 1898). 
The marginal plates generally number only 4 in each interradial 
Space, besides a pair of much larger plates at the end of the arms. 
They afe more or less swollen, bean-shaped and surrounded by a 
regular series of small grains like those surrounding the plates 
of the disk. Sometimes a small plate is developed in the midline 
between the marginal plates, in the corner between each four 
adjoining plates; sometimes also a pair of small plates are devel¬ 
oped close to the end-plates of the ray. The end-plates ( the 
term “apical plates” used by Hutton, Farquhar and Benham 
is not very fortunate —) may be very much enlarged and highly 
swollen, so as to be several times larger than the other marginal 
plates; but in other specimens they are much less enlarged. 
