OF ARTS AND SCIENCES. 195 



The most common species of the Brissina is Hemiaster cavernosus, 

 which occurs in large number in moderately deep water at the 

 Kerguelen Islands, the southern extremity of South America. Hemi- 

 aster gibbosus is a Pacific species, of which H. zonatus is the Atlantic 

 representative. The northern Brissopsis lyrifera and Schizaster 

 fragUis are found in the South Indian Ocean. The Pacific Schi- 

 zasteridse were S. claudicans, S. ventricosus, and S. japonicus, while 

 S. Philippii ranged from the southern extremity of South America 

 through the South Pacific to the Southern Indian Ocean. 



The following are the main points of the bathymetrical distribution 

 of the Echini of the Challenger expedition. 



Among the Cidarid^e, Cidaris proper, Phyllacanthtcs, Stephano- 

 cidaris, and Goniocidaris are littoral, and extend but little beyond the 

 100-fathom line; though G. canaliculata has been found to 1,700 

 fathoms. 



Dorocidaris extends to a depth of 600 fathoms, while Porocidaris 

 was not found in less than 400 fathoms, and extended to a depth of 

 nearly 2,000 fathoms. 



The Salenid^e extend from the 100-fathom line to 1,850 fathoms. 



In the Arbaciad^e the species of Arbacia proper are littoral, and 

 are found to a depth of 150 fathoms ; from 80 to somewhat over 100 

 fathoms extends Ccelopleurus, while the species of Podocidaris are 

 the deep-water forms of this family, with a range of from 400 fathoms 

 to nearly 1,100. 



Among the Diademetidje, Diadema and Echinothrix are strictly 

 littoral, while Astropyga and the new genus Micropyga, closely allied 

 to it, occur quite frequently from 75 fathoms to 250 fathoms, and 

 even occasionally to a depth of 600. The genus Aspidodiadema com- 

 mences at a depth of 100 fathoms, takes a greater development at 

 about 600 to 700 fathoms, and has been found at a depth of over 

 2,200 fathoms. This genus, with the species of Asthenosoma and 

 Phormosoma, are the deep-water types of the family, and of the 

 Echinothurue, for although one of the species of Asthenosoma 

 occurs in ten fathoms, the larger number of the species of the genus 

 are not found in less than 100 fathoms, the greater number occurring 

 in 200 to 300 fathoms and extending to 2,600 fathoms. The species 

 of Phormosoma collected by the Challenger are found mainly in 

 from 250 to 1,000 fathoms, being still common from 1,000 to 2,000 

 fathoms, and found as deep as 2,750 fathoms. 



The Echinometrad^e are all shallow-water species, no species 

 extending beyond the 100-fathom line. 



