ECHINOIDEA 643 



C. antiUarum (Philippi) {Diadema setosum Gray). Spines black, 

 very slender and long, and poisonous ; diameter 8 to 10 em. : Florida 

 and West Indies ; very common in shallow water among rocks and corals. 



Family 3. ARBACIIDAE. 



Sea-urchins with a circular outline and with peristomal gills; spines 

 solid and rather large; ambulacral areas narrow; aboral ambulacral feet 

 without suckers: 7 genera and 18 species. 



Arbacia Gray. Subglobular or pyramidal sea-urchins; interrays 

 naked at the aboral end: 5 or 6 species. 



A. punctulata (Lamarck) (Fig. 988). Color reddish-brown; diame- 

 ter 3 to 5 cm. ; height 15 to 25 mm. ; length of spines 20 to 25 mm. : Cape 

 Cod, southwards to Yucatan, from low- 

 water mark to 120 fathoms; common. 



Family 4. ECHINIDAE. 



Sea-urchins with a circular outline, 



with peristomal gills and a single pair 



of ambulacral plates at the base of each 



ray in the peristome; each ambulacral 



plate with 3 pairs of pores; periproct 



composed of numerous plates: 9 genera 



and more than 50 species. Fig. 988 — ArMcia punctulata — 



^ , . . • /„ oral aspect (Coe). 



1. Lytechinus a. Agassiz {Toxop- 



neustes Agassiz). Spines short; tubercles all of about the same size and 

 in several rows; peristome large: 8 species. 



L. variegatus (Lamarck). Diameter 5 to 8 cm.; height 3 to 4.5 cm.; 

 color green, often with more or less purple; spines rather short and 

 slender: North Carolina to Brazil, from low-water mark to 30 fathoms. 



2. Tripneustes Agassiz {Hipponpe Gray). Large sea-urchins with 

 a thin shell and numerous small tubercles on which are small spines: 

 3 species. 



T. esculentus (Leske). Test 10 to 15^ cm. in diameter, semi-globular; 

 color white: South Atlantic coast and West Indies; used for food by the 

 West Indian negroes. 



Family 5. STRONGYLOCENTEOTIDAE. 



Sea-urchins with a circular outline; 4 to 11 pairs of pores in each 

 ambulacral plate: 8 genera and about 30 species. 



Strongylocentrotus Brandt. Spines slender and fluted ; tubercles 

 not all of the same size, arranged in numerous series and often crowded : 

 about a dozen species. 



