OF ARTS AND SCIENCES. 197 



down to the depth of 2,300 to 2,900 fathoms ; the genera Palceotropus 

 and Cionobrissus being limited to a less depth than 1,000 fathoms, 

 while Aerope, Calymne, and two or three species of Pourtalesia, are 

 found within these limits, but also extend to the greatest depth at 

 which any Echini have been found, viz. 2,900 fathoms. 



The genera Spatagocystis, Echinocrepis, Genicopatagus, Ur echinus, 

 and Cystechinus, range mainly between 1,300 and 2,000 fathoms, 

 one of the species of the latter genus extending to 2,225 fathoms, 

 while Aceste has only been found in 2,600 fathoms thus far. 



Paleopneustes occurs in the neighborhood of 300 to 400 fathoms, 

 and Homolampas is found at a depth of 400 fathoms and over. 



Among the Spatangina, the northern Spatangus purpureus is 

 found in the tropics at a depth of 450 fathoms. Eupatagus , Lovenia, 

 Breynia, and Maretia planulata are strictly littoral, not extending 

 beyond a depth of 28 fathoms. Maretia alta has been found to ex- 

 tend to a depth of 800 fathoms ; and the species of Echinocardium, 

 like those of Brissopsis, although littoral, yet extend to great depth, 

 one species, Echinocardium Jlavescens, to 150 fathoms, while E. 

 australe has come up from no less than 2,675 fathoms. The only 

 species of the genus Argopatagus was found at a depth of 800 

 fathoms. 



Among the Brissina, Rhinobrissus, Periaster, Metalia, and some 

 species of Schizaster, are either littoral or do not extend to the 100- 

 fathom line, or but little beyond it. The species of Schizaster, how- 

 ever, reach a considerable depth ; in one case 1,375 fathoms, in another 

 800, and in a third 345 fathoms. The species of Hemiaster, also, greatly 

 vary in their bathymetrical range, the two species most closely allied 

 to the cretaceous Hemiaster prunella extending from 340 to 800 fath- 

 oms, while Hemiaster cavernosus ranges from 15 to 400 fathoms. In 

 Brissopsis lyrifera the bathymetrical range extends from 15 to 1,100 

 fathoms. The Mediterranean Brissus unicolor extends to a depth of 

 450 fathoms. 



Dorocidaris bracteata, A. Ag., nov. sp. 



This species is closely allied to Dorocidaris papillata. It is charac- 

 terized by the small papilla? covering the abactinal area, the small 

 size of the mammary boss of the primary tubercles, and the greater 

 distance between the primary tubercles compared with the Atlantic 

 species, D. papillata. The primary radioles are fluted, with a more or 

 less serrated edge. The ambulacral system is also relatively much 



