80 PORCELLANASTERIDAE. 
himself describes four new species in his relatively brief paper. But the omis- 
sion is not serious for the present species is notably distinct and might well be 
made the type of a new genus. It resembles S. chuni and S. paucispinus in 
the large disk and short arms; the general facies is thus very different from that 
of the typical members of Styracaster. But the absence of paxillae and the 
presence of only five narrow eribriform organs distinguishes monacanthus at 
once from its two nearest allies and these differences are accentuated by the 
very low and wide interradial marginal plates and the presence of only a single 
spine on the supramarginal series of plates of each arm. The low, rounded 
scale-like spines on the margin of the oral plates are an added feature worthy 
of note. The disk is light gray and the arms and marginal plates are nearly 
white, in slight contrast. 
Station 4701. Eastern Tropical Pacific, 19° 11’ 30” S., 102° 24’ W., 2,265 fms. Bott. temp. 35.5°. 
Dk. br. choc. c., mang. nod. 
One specimen. 
Styracaster paucispinus. 
Plate 2, fig. 3, 4. 
Lupwie, 1907. Zool. Anz., 31, p. 315. 
Ludwig’s description of this species is somewhat more ample than that of 
monacanthus but as in the case of that species, he does not discuss its relation- 
ships. It agrees with S. armatus, spinosus, and edwardsi in the possession of 
only three cribriform organs in each interbrachial arc; in the great breadth of 
these, paucispinus is nearest to armatus. But it differs very markedly from all 
these species, in its very short arms, R equalling 2.5r or less, whereas in the three 
other species, R = 3r or more. Associated with this shortness of arms is a 
reduction in the number of superomarginal spines which are never more than 
three to an arm and may be one only; Ludwig says ‘‘two or three” but I fail to 
find more than two in any case; the longest ones are scarcely 2 mm. high and 
are quite thick at the base. The “winzigen, granuloiden stachelchen” on the 
ventrolateral plates are so minute as to hardly warrant the name, and in one 
specimen appear to be quite wanting. The adambulacral plates have a marked 
depression or shallow furrow on the ventral surface; this runs from the inner 
adoral corner of the plate, where it is deepest, to the outer aboral corner, where 
it flattens out entirely. 
