BATHYMETRICAL DISTRIBUTION. 



In the following tables the species are grouped according to the bathymetrical zones 

 in which they occurred. I have thought it unnecessary to incorporate the results of 

 other and later deep-sea expeditions, for so far as is known from what has already been 

 published on the subject, these do not add materially to the results obtained by a study 

 of the Challenger collection. 



I have followed Professor A. Agassiz in considering all depths beyond 500 fathoms 

 as abyssal, but this limit must be regarded as a somewhat arbitrary one. There is less 

 difficulty in deciding where the littoral fauna ceases and the deep-water forms make 

 their appearance, and as regards the Anomura at least, the 100 fathom line marks 

 approximately the boundary between the two. 



The Anomura, it may be stated generally, occupy an intermediate position between 

 the Macrura and the Brachyura, in regard to the limit of depth at which they are found. 

 The more highly specialised forms are like the Brachyura found in shallow-water and 

 moderate depths, whereas the more primitive Macruran types extend to the abysses of 

 the ocean. Mr. Miers has pointed out that the Brachyura obtained from the greatest 

 depths are essentially those most nearly related to the Anomura.. 



The tables, in addition to affording a list of the species taken at different depths, 

 indicate the relative proportion of new species obtained in each vertical zone. It will 

 be seen that a large proportion of the deep-water and abyssal forms belong to previously 

 undescribed species — indeed all of the latter, with a single exception, were taken for 

 the first time by the Challenger ; though in the long interval that has elapsed since the 

 return of the expedition, subsequent deep-sea investigations have resulted in the redis 

 covery of several. 



One or more numbers placed after any species indicate that it was also obtained 

 from the corresponding zones. 



Terrestrial Species. 



Birgus latro (Linne). 

 Ocenobita clypeata (Herbst). 



Ccenohita rugosa, H. Milne-Edwards. 

 „ perlata, H. Milne-Edwards. 



