SEA-URCHINS 223 



FAMILY ECHINOMETEID.S: 

 In this family the ambulacral plates have several pairs of pores. 



GENUS Echinometra 



E. subangularis. This species, which ranges from South Carolina 

 to Brazil, and is also found in Bermuda, is common on mud-flats and is 

 easily distinguished by its oblong or elliptical shape. Its shell is about 

 three inches long in its widest portion. The spines are one half of an 

 inch to one inch long, thick at the base and tapering to a point. The 

 color is dark purplish-green to deep violet almost black. 



GENUS Strongylocentrotus 



S. drobachiensis. This sea-urchin (which bears, perhaps, the longest 

 name in technical nomenclature and has no other, unless that of " sea- 

 egg," which is applied indiscriminately to all sea-urchins) is a very com- 

 mon species in shallow waters of the northern temperate zones. It 

 extends as far as New Jersey on the Atlantic and to the State of Wash- 

 ington on the Pacific coast. Although it is found as far south as New 

 Jersey, it is there rare and small; but farther north, especially on the 

 coast of Maine, it is exceedingly abundant. It is green or greenish - 

 purple in color, and resembles somewhat a large chestnut-bur. The 

 body is circular, somewhat depressed (but of variable thickness), and 

 about two inches in diameter. The spines are moderately slender and 

 longitudinally striated. It feeds partly on diatoms and other small 

 algae, which it cuts from the rocks with its sharp teeth. It also devours 

 dead fishes, bones and all, and in return is swallowed whole by the wolf- 

 fish and other large fishes. It moves by means of the tube-feet on its 

 oral surface, slowly dragging itself along, and frequently is seen with 

 seaweed, a stone, or some other substance on its back, which it places 

 there with its pedicellarise for the purpose of concealment. 



S. pur^turatus. The common purple sea-urchin of the west coast, 

 from Sitka to Lower California, found in abundance on the rocks just 

 beyond low-water mark. It is about one and a half inches in diameter, 

 with rather thick, pointed, and fluted spines. 



S. franciscanus. This is the largest species of the west coast, the 

 shell measuring sometimes five inches across, and the thick spines one and 

 a half inches in length. The tubercles on the naked shells are very promi- 

 nent, and the zones are very clearly marked. It is purple in color and 

 is often found in great quantities at low-water mark. It ranges from 

 Alaska to Lower California. (Plate LVII.) 



FAMILY ECHINIDJE 



In this family the ambulacral plates have but three pairs of 

 pores. 



