RECORDS OF W.A. MUSEUM. 
136] 
PENTAGON ASTER STIBARUS, 1 sp. nov. 
Plate XVII. 
Rays 5. R=52 mm., r=28 mm. R 2r. Interbrachial arcs 
well rounded. Rays broad and flat. Breadth at base, 29 mm. 
Disc large, very little arched ; vertical diameter only about 13 mm. 
Superomarginal plates, 40, that is, eight on each side or four on each 
margin of each arm ; the terminal pair the largest and much swollen ; 
the others are subequal and little swollen. Each plate is surrounded 
by a single, double or even triple series of minute, crowded, flat- 
topped granules, but the surface of each plate is perfectly smooth. 
Inferomarginals 60, that is, twelve on each side or six on each 
margin of each arm ; on each side of the starfish, the six median 
inferomarginals correspond exactly in position with the superomar- 
ginals above them, but the swollen terminal superomarginal overlies 
three inferomarginals, of which the antepenultimate (and not the 
penultimate nor the last) is the largest and is slightly swollen. The 
penultimate is distinctly smaller but is equally swollen, while the 
last is quite small and is almost or quite flat. The inferomarginals 
are smooth and surrounded by granules exactly as are the supero- 
marginals. 
The plates covering the abactinal surface are smooth, polygonal 
or rounded and surrounded, like the marginals, by a series of flat- 
topped granules. The largest are in the interradial areas and are 
four or five millimetres across ; the smallest are near the tips of the 
rays. Distally, the median radial series are slightly swollen, while 
proximally, in the type (the larger specimen), each plate bears a 
blunt low spine, or high tubercle. Two or three plates not in the 
median radial series, but near the centre of the disk, bear similar 
but small tubercles. In the smaller specimen (R— -41 mm.) such a 
tubercle is indicated on only one plate, the dorso-central, while the 
five primary interradial plates are much larger and more conspicuous 
than in the type. In both specimens, the rounded triangular mad- 
reporic plate lies just distal to one of the primary interradials ; in 
the type, it is much swollen. 
The actinal surface is covered by polygonal plates similar to 
those of the abactinal side and like them surrounded by series of 
granules. Adjoining each mouth angle is a single plate, distal to 
1 Gr. stibaios — compact, sturdy. 
