WEST INDIAN STARFISHES 111 



The paxilliform dorsal plates are thick and have slightly lobed 

 bases (usually six lobes) ; they are united by these lobes, with- 

 out intermediate ossicles, and have isolated papular pores in the 

 intervening spaces; the median radial row is distinct but like 

 the others. On the disk the five interradial primary plates are 

 much larger than the others, round, tabulate, and spinulose. 



The marginal plates are separated by deep ciliated grooves, 

 but are not fasciolated. 



Only one species of the genus is known. 



RosASTER ALEXANDRi Pcrrier. 



Pentagonaster alexandri Perrier, Bull. Mus. Comp. ZooL, ix, p. 22, 1881. 



Nouv. Arch, du Mus., vi, p. 238, pi. vi, figs. 3-8, 1884. 

 Eosaster alexandri Per., Exp. Sci. Trav. et Talism., EiChinod., p. 387, 1894. 



Verrill, Envision Genera and Species of Starfishes, p. 197, 1899. 



Plate xi ; figures 3 — 3h, details. Plate xvii ; figure 2. 



Form small, stellate, with a large disk, incurved sides, and 

 rays tapering to slender tips. Radii of a specimen taken off 

 Havana, by the Bahama Expedition, and 15™°^ ; ratio, 1 :2.12 ; 

 marginal plates nine, large. 



The six superomarginal plates that form the evenly incurved 

 margin of the disk are distinctly larger than those on the rays; 

 they are wider than long, convex, and rise above the paxillar area, 

 forming a stout border. Those on the rays are at first rectangu- 

 lar but decrease rapidly in size and become square. Seven pairs 

 are in contact medially. Ocular plate is broad ovate, not 

 notched above. The marginal plates are covered with spaced 

 small, short, rough spinules, smaller and acute above, larger and 

 more obtuse or clavate on the outer side and along the margins 

 of the sutures, which have deep grooves, but are not f ascioled. 



The dorsal paxillar area is pentagonal, not extending beyond 

 the basal radial plates. The radial areas are covered with regu- 

 larly stellate parapaxillae, which have a thick six-lobed base and a 

 short cylindric, or slightly tabulate, central boss or column, 

 surmounted by a divergent stellate group of about eight to ten 

 short slender spinules, surrounding a larger, slightly spiniform 

 central one. The spinules are very regularly arranged, and are 

 minutely thorny at the tips. In each of the intervals between 

 the basal lobes there is a papular pore. In the interradial area 



