48 



ASTEROIDEA. 



10. Genus. — Oreaster, JM. and T. = Penfaceros, Linck. ; Goniaster, Agass. (pars). 



Fig. 24. 



Upper surface of Oreaster turritus, Linck. 



Under side flat, upper surface more or less 

 elevated ; the middle of the rays ridged with 

 an angular, or strongly inflated, keel. Two rows 

 of granular marginal plates ; the border is formed 

 by the upper row, and the lower row lies at the 

 under surface. The body is everywhere covered 

 with smaller or larger plates, Avhich, with the mar- 

 ginal plates, are either entirely granular, or some- 

 times carry more or less spinous tubercles ; the 

 pore-fields between the plates of the upper surface 

 are graiailated with many pores. PedicellariaB 

 sessile, either valve-like or pincers-like ; vent sub- 

 central. 



11. Gemis. — AsTROGONiUM, M. and T. = Pent agon aster, Linck. ; Goniaster, Agass. 



Body pentagonal, disc-shaped, flat on both sides. Two rows of marginal plates, which 

 are much larger than the other plates of the body. Both rows contribute to the formation 

 of the margin. Their border is surrounded by a wreath of granules, or their circumference 

 is encircled by granules. Up to this enclosure they are completely naked. Sometimes 



Fig. 25. Fig, 26. 



A. B. 

 Astrogonium, sp. Brit. Mus. Col. 



they carry tubercles upon the middle. The upper and under surfaces are tesselated with 

 free-lying plates ; between these only narrow, granulated pores have places ; vent sub- 

 central. 



