IIO CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



and interambulacral area. Scattered thickly among the primary- 

 spines are much smaller, secondary, spines of similar shape, 

 while a third*variety, the miliary spines, are still smaller and very 

 slender. There are five pairs of buccal plates, which bear miliary 

 spines. The comparative sizes of the spines and their arrange- 

 ment are well shown by the tubercles on the test (Plate XXI). 

 Several kinds of large fishes, including the wolf-fish, swallow 

 the adult animals whole, quite disregarding the sharp spines 

 which cover the body. The young have still more numerous 

 enemies among the fishes, and the free-swimming plutei are 

 swallowed in great numbers by surface-feeding fishes. 



Echinarachnius parma (Lamarck) 

 Sand-dollar 



Plate XXIII ; Plate XXIV, fig. 2 ; Plate XXVII. 



The sand-dollar is a most interesting little creature because 

 of its peculiar modifications to meet the requirements of the 

 environment under which it lives. It is sometimes very abun- 

 dant on sandy bottoms off shore, where it lives partly buried 

 beneath the surface of the loose sand. The body is covered with 

 a multitude of tiny suckers, by means of which the creature 

 creeps slowly along, devouring as it goes particles of sand with the 

 numerous microscopic organisms, particularly diatoms and other 

 algae, which are found among them. 



The much flattened, disk-like body is well adapted for with- 

 standing any tendency to be rolled over or thrown upside down 

 by the shifting of the sand under the influence of the waves. 

 It is very probable, moreover, that the animal can penetrate 

 deeper into the sand when the water becomes very rough, to 

 return to the surface again after the disturbance is over. 



The species has a remarkable range of distribution. It is 

 found along the Atlantic coast from Labrador to New Jersey, and 



EXPLANATION OF PLATE XXVII. Echinarachnius parma. Aboral and 



oral surfaces. (Natural size.) 



The aboral surface, upper figure, shows the minute spines and the 

 darker ambulacral areas, " petals " The oral surface, lower figure, shows 

 the ambulacral areas as narrow furrows radiating from the centrally 

 placed mouth and branching on each side toward the margin. These 

 areas are nearly devoid of spines. A cluster of less slender spines sur- 

 rounds the mouth. 



