HABITS OF ECHINI. 707 



The Clypeastroids are mainly found in sand, considerably below low- 

 water mark, though .some of the species seem to thrive on the edge of that 

 line, where they are exposed to the full force of the surf on open sandy 

 beaches. Echinarachnius parma, Echinarachnius excentricus, Mellita testudi- 

 nata, and Mellita longifissa are quite common in certain localities at low- 

 water mark, where the force of the breakers is very considerable. As a gen- 

 eral rule, however, the Clypeastroids, as well as Spatangoids, prefer quiet 

 sandy bottoms, in which they bury themselves. All the Echini, as far as 

 known, are more or less gregarious ; those who have had occasion to collect 

 on our rocky shores cannot fail to have noticed how sea-urchins are fre- 

 quently crowded, in favorable localities, over the surface of the rocks, so 

 as literally to pave the bottom of sheltered rocky pools. Professor Verrill 

 has also brought up from deep water our common sea-urchin in large num- 

 bers at a single haul of the dredge. The same is the case with our more 

 southern species. Echinarachnius, Encope, Mellita. Eeliinanthus, are all 

 gregarious. The few Spatangoids I have had occasion to observe alive — 

 Meoma, Moira, Echinocardium, Rhynchopygus — are all found in numbers. 

 As has been observed by Thomson and Jeffreys, in some localities, in deep 

 water the dredge has come up filled with thousands of specimens of Echinus. 

 (Maris, though not very numerous along the shores and in shallow water, 

 appears in deeper water to be gregarious, as large numbers of Dorocidaris have 

 been brought up at a single haul of the dredge by Mr. Pourtales from con- 

 siderable depths. No dredging can be done on sandy bottoms along points 

 of our coast without bringing up large quantities of Echinarachnius. 



The same has been Stimpson's experience in the China Seas with Echina- 

 rachinus mirabilis, which frequently covers the bottom of the sea for con- 

 siderable distances. Colobocentrotus, he also says, occurs in great numbers. 

 A coral reef literally bristles with Diadematidae, and cavities in the more 

 sheltered spots are filled with them. The Echini serve as food for fishes with 

 sufficiently powerful jaws. Our cod and haddock are great eaters of the 

 two more common species of sea-urchins of New England. 



