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



enormous size. By means of the tube-feet the creature clings 

 to the objects on which it rests and crawls slowly about. In 

 the center of the body is the pentagonal mouth with the five 

 calcareous teeth, and extending across the body are three bands 

 of cilia which are thought to serve in sweeping towards the 

 mouth the small particles of organic matter on which the animal 

 feeds. With the increase in size of the body the ciliated bands 

 disappear, and the now relatively minute tube-feet 'convey the 

 food to the mouth. As the disk-like body of the animal increases 

 further in size, the anal opening, which is at first on the aboral 

 surface, is gradually shifted to the edge of the disk. The en- 

 largement of the disk now becomes interrupted at certain points 

 on the periphery, causing five notches in the margin. By con- 

 tinued growth of the intervening portions the notches become 

 elongated, and their edges close together and unite distally, to 

 form the characteristic lunules. 



KEY TO SPECIES 



The echinoids of the world are divided into three orders : ( I ) 

 Regularia, including the hemispherical sea-urchins; (2) Cly- 

 peastroidea, including the flat and disk-like forms; and (3) 

 Spatangoidea, or heart-urchins. 



The two first orders only are found in Connecticut waters, 

 and of these there are four representatives ; two, the purple sea- 

 urchin and the green sea-urchin, belonging to the Regularia, and 

 two, the sand-dollar and the key-hole urchin, to the Clypeas- 

 troidea. They may be easily distinguished by the following 

 characters : — 



1. Body nearly hemispherical, spines rather large, anal opening 



at aboral pole 2 



Body flat and disk-shaped, spines small, anal opening ec- 

 centric 3 



2. Spines long, absent near aboral pole . . . Arbacia punctulata 

 Spines short, covering aboral pole 



Strongylocentrotus drobachiensis 



3. Test without perforations Echinarachnius parma 



Test with five narrow perforations (lunules) - 



Mellita pentapora 



