REPORT ON THE ECHINOIDEA. 



243 



into the abyssal fauna ; and the following continental species have an extreme range of 

 more than 1000 fathoms : — 



1000 fathoms. Finally, of the abyssal species the following have a greater range than 

 1000 fathoms : — 



Aspidodiadema inierotahercalatum, 

 Pourtalesia Jaguncula, 

 Galymne rclirta, 

 Homolavipas fnujilis, 



804-2225 fatlioms. 

 34.5-2900 

 620-2650 „ 

 300-1920 



and quite a numl^er of other species of which the range approaches 1000 fathoms but is 

 below it, showing thus that a very large proportion of the known Echinids have an ex- 

 traordinary l)athymetrical range, and that distributed as these are among all the families 

 and principal groups of Echinids, it is evident we cannot look upon pressure alone as 

 a very important feature in the limitation of the l^athymetrical range, but that we must 

 rather look to the difference of temperature characterising the three belts here recognised 

 as the principal element in the distribution of the Echinids in the depths of the ocean. 



The genera characteristic of the littoral faunae which disappear from the continental 

 limits, exclusive of the species having a great bathymetrical range, are the greater 

 number of the species of Cidaridee — 



Cidaris. 

 Phyllacanthus. 



The greater number of the Diadematidse- 



Diadema. 

 Centrostephcmus. 



All the Echinometradse — 



Colobocentrotus. 



Heterocentrotus. 



Echinometra. 



Pavasalenia. 



Stomopneustes. 



Stephatiocidaris. 

 Arbacia. 



Echinoilirix. 

 Astropyga. 



Strongylocentrotus. 

 SphcBrechinus. 

 Pseudoboletia 

 Echinostrephus. 



