12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I49 



habited by large individuals of Diadema antillarum. Sandy patches in 

 large depressions and grooves contain few Clypeaster subdepressus. 

 Echinoneus cyclostomus and Brissus unicolor live under slabs of reef 

 debris in and near the reef. 



Outer edge of reef, and sandy terrace. — (Stations 16, 18, 19, 37, 

 61 ) depth 25-50 feet ; tongues of sand extending from sandy terrace 

 up through steep-sided grooves in lower edge of reef ; sand fairly 

 clean, with rocky patches, burrows by burrowing fish, some algae, 

 broad ripples. Echinoids in sand: Clypeaster subdepressus (buried 

 deeply), Meoma ventricosa, Schizaster (Paraster) floridiensis, 

 Brissus unicolor, Echinoneus cyclostomus. Echinoids in holes in 

 rock: Diadema antillarum (abundant), Echinometra viridis (one 

 specimen). 



Level sand flats beyond reef. — (Stations 17, 17a, 36) depth 80-85 

 feet; bare sand with thin cover of algae in patches, rocky holes of 

 burrowing fish, small piles of rock supporting sponges and small 

 corals ; echinoids : Eucidaris tribuloides, Diadema antillarum (small, 

 among rock and sponges), Astropyga magnifica (in groups, on sand), 

 Clypeaster subdepressus (small, many dead, few alive), Meoma 

 ventricosa, Plagiobrissus grandis (dead), Brissus unicolor, Schizaster 

 {Paraster) floridiensis (dead). 



Deep water beyond 85-foot terrace. — (Station 25) depth 105-110 

 feet ; large mounds of living coral, with sponges, fish, crinoids, basket 

 stars, mounds about 50 feet long, 12 feet high, surrounded by coarse 

 sand of shell and calcareous algal debris. Very large Diadema antil- 

 larum in niches in coral mounds ; no echinoids observed in sand. 



SYSTEMATIC DISCUSSION OF SPECIES 



Descriptions, synonymys, and illustrations of the species discussed 

 below can be found in Mortensen (1928-1951). 



Order Cidaroida Claus 



Family CIDARIDAE Gray 



Genus EUCIDARIS Pomel 



EUCIDARIS TRIBULOIDES (Lamarck) 



Plate 2, figures 1-3 ; text figure 7 



This large brown urchin is easily recognized by its long thick spines 



arranged in 10 vertical series. It has a globular shape and is locally 



known as the mine or satellite urchin. An adult is approximately 



100 mm. in horizontal diameter with its spines, 50 mm. without. The 



naked test is characterized by straight, narrow poriferous zones with 



only two vertical rows of pore-pairs in each ambulacrum, and broad 



interambulacral areas with 10 vertical series of large tubercles. 



