246 THE VOYAGE OF H.M.S. CHALLENGER. 



Calymne. lAnopneustes. 



Palceotroiyus. Cionohrissus. 



Genicojyatagus. Aerope. 



Homolampas. Aceste. 



That is,^we have 16 genera which are eminently abyssal out of the 24 genera extend- 

 ing into the abyssal region, exclusive, of course, of the species which have an abnormal 

 bathymetrical range and spread from the littoral to the greatest depth at which Echinids 

 have been dredged. The abyssal genera belong nearly all to a new group of Spatangoids 

 related to those of the Chalk and have no allies among the littoral species. 



Geographical Range of the Continental and Abyssal Species. 



As regards the geographical range of the continental, and of the abyssal species, we 

 have, unfortunately, no data for the Indian Ocean, and we must therefore limit our com- 

 parisons of geographical distributions entirely to the littoral faunae thus far recognised 

 in the Atlantic and Pacific. 



Examining in the first place the continental species by themselves, we find a far greater 

 proportion of representative species among the Atlantic and Pacific continental species 

 than we find when comparing the corresponding littoral faunae; and if we take, as perhaj)s 

 belonging to the continental species, a few species of which only a few or single siDecimens 

 were collected, the representative character of the Atlantic and Pacific continental 

 geographical fauna; is cj^uite stiiking. 



We find both in the Atlantic and iu the Pacific species of Poroeidaris, Salenia, 

 Podocidaris, Ccelopleurus, Aspidodiadema, Asthenosonia, Phormosoma, Trigonocidaris, 

 Echinus, Paleopneustes, Rhinohrissus, Agassizia, Schizaster, and Periaster. 



Such species as Goniocidaris may belong perhaps to the littoral range ; we have left 

 thus far among the continental species characteristic of the Atlantic only a small 

 number of genera, Temnechhms, Hemipyedina, Neolampus, Conochjpus, and as 

 characteristic of the Pacific continental ranges Micropyga, Catopygus, Nacopatagus, and 

 Moiropsls. A condition of things totally unlike that is found when comparing the same 

 districts with regard to the occurrence of the same genera. That is, among 22 genera of 

 the continental range 14 are represented both in the Atlantic and Pacific, while there 

 are thus far four clistintly Pacific genera, and as many Atlantic ones, while of the littoral 

 faunae, only six are characteristic of the Atlantic, 31 genera as common to both, and 36 

 are thus peculiar to the Pacific. 



When we examine the abyssal species, leaving out of consideration the few which 

 may perhaps belong to the continental range, of which we have not sufiicient data, such 

 as Podocidaris, Aspidodiadema, Prionechinus, Cottaldia, Pygaster, and Linopneustes, 

 we find as common to the Atlantic and Pacific the following genera : — Asthenosoma, 



