SEA-URCHINS 223 
FAMILY ECHINOMETRDE 
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 
algee, 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 pedicellarie for the purpose of concealment. 
S. purpuratus. 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 inlength. 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 ECHINIDE 
In this family the ambulacral plates have but three pairs of 
pores. 
