240 



THE VOYAGE OF H.M.S. CHALLENGER. 



CiDARiD.E (2 species). 

 Porocidaris, 2. 



Arbaciad^ (2 species). 

 Podocidaris, 2. 



Diadematim; (2 species). 

 Aspidodiadevia 2. 



ECHINOTHURID/E (11 SpCcies). 



Asthenosoma, 2. 

 Phormosoma, 9. 



Temnopleurid^ (3 species). 

 Prionechinus, 1. 

 Cottaldia, 1. 

 Jrtgonocidaris, 1. 



Or twenty species of Desmosticha representing nine genera. 



The Clypeastridse have completely disappeared with the exception of Pygaster (this, 

 however, like a few other species here included in the abyssal list may hereafter prove to 

 belong to the continental fauna) and of the few littoral species having great bathy- 

 metrical range. 



Among the Petalosticha we find a great development of species of genera represented 

 in the Tertiary and Cretaceous periods. Of the Desmosticha the families characteristic of 

 the littoral faunae have either completely disappeared or are but scantily represented by 

 genera with an ancient geological facies, or genera having a considerable range in time. 

 We find the Petalosticha distributed in the following genera : — 



Brissina (7 species). 

 Cionobrissus, 1 . 

 Aerope, 1. 



Aceste, 1. 

 Hemiaster, 4. 



AVhile all the other species (twenty-two) belong to the typical deep-sea groups of 

 Pourtalesise and Ananchytidse distributed in tlie following genera : — 



Pcdceotropus, 2. 

 Homolampas, 2. 

 Linopneustes, 1. 

 Argopatagus, 1. 

 Urechinus, 1. 

 Cystechinus, 3. 



Calymne, 1. 

 Genicopatagus, 1 . 

 Echinocrepis, 1. 

 Spatagocystis, 1 . 

 Pourtalesia, 8. 



Or twenty-nine species of Petalosticha distributed in fifteen genera. 



In each one of the bathymetrical belts- we have- recognised, we find, as an inspection 

 of the table will show, an encroachment at both the upper and lower limits of each zone- 

 by exceptional species, which wander into far greater depths, and become associated in 

 succession with the species of the preceding and succeeding zones, and thus modify to a 

 considerable extent the characteristic physiognomy of each bathymetrical belt. 



