EEPORT ON THE HEXACTINELLIDA. 455 



BATHYMETRICAL DISTRIBUTION OF THE CHALLENGER 



HEXACTINELLIDA. 



In order to afiford a ready survey of the main results of the Challenger Expedition in 

 regard to the bathymetrical distribution of the Hexactinellida, I have compiled Table 

 VIII. , in which the horizontal divisions mark out intervals of depth of 100 fathoms each 

 from 100 to 1000 fathoms, and of 500 fathoms each from 1000 to 3000 fathoms, while 

 the vertical columns correspond to the four families of Lyssacina, and the two main 

 divisions of Dictyonina, the Uncinataria and Inermia. 



This table shows distinctly that Hexactinellida occur in varying abundance only from 

 about 100 (more exactly 95) up to 3000 (more exactly 2900) fathoms. 



Thus the previously determined character of the Hexactinellida as specifically, and in 

 fact exclusively, deep-sea forms is indubitably established, and the maximum depth 

 previously known (2410 fathoms according to Agassiz) is exceeded by several hundred 

 fathoms, with a maximum of 2900. 



In order to express clearly the bathymetrical distribution of the Hexactinellida in 

 the different oceans, it is convenient to tabulate not only for the whole group, but also 

 for the several divisions, the statistics of depth and abundance, both in their absolute 

 and percentage relations. This is done in the following table : — 



