194 Mr. S. I. Smith on (he Abyssal 



scarlet or vermilion ; but such bright markings were not 

 noticed in any species from below 1000 fathoms. Below 

 this depth orange-red of varying intensity is apparently the 

 most common colour, although in several species, very notably 

 in Noiostomus robustus, the colour is an exceedingly intense 

 dark crimson. 



The structure of the eyes of the abyssal Decapoda is of the 

 highest interest, and worthy of the most minute and careful 

 investigation and comparison with the corresponding struc- 

 tures of shallow-water species. Such an investigation I have 

 not been able thus far to make ; but the importance of the 

 subject induces me to record the results of a superficial exa- 

 mination of the external characters of the eyes of most of the 

 abyssal species from the ' Albatross ' collections. 



If we exclude from this examination all the species whose 

 bathymetrical habitat is in any degree doubtful, and examine 

 the twenty-one species given as inhabiting the immediate 

 neighbourhood of the bottom, we find that Geryon quinquedens, 

 Lithodes Agassizii, and Sabinea princeps have normal well- 

 developed large black eyes, apparently entirely similar to those 

 of the allied shallow-water species ; Sclerocrangon Agassizii, 

 Bythocaris gracilis, Heterocarpus oryx, Nematocarcinus ensi- 

 ferus, and N. cursor have normal black eyes a little smaller 

 than the allied shallow-water species ; Ethusina abyssicola 

 and Parap>agurus pilosimanus have distinctly faceted black 

 eyes, which, though very much smaller than in most shallow- 

 water species, are still fully as large and apparently quite as 

 perfect as in those of some shallow-water species, in which 

 they are evidently sensitive to ordinary changes of light. The 

 eyes of the species of Glyphocrangon are very large, with the 

 faceted surface much larger than in the allied shallow-water 

 species ; but they are borne on very short stalks with compa- 

 ratively little mobility, and have dark purple instead of black 

 pigment ', the eyes of Pontophilus abyssi are lighter in 

 colour than those of the species of Glyphocrangon, but are 

 faceted and apparently have some of the normal visual 

 elements ; all the species of Munidopsis and Pentacheles have 

 peculiarly modified eyes from which the normal visual elements 

 are apparently wanting. Of these twenty-one abyssal species, 

 eight are thus seen to have normal black eyes, two have 

 abnormally small eyes, and three have eyes with purplish or 

 very light-coloured pigment, while eight have eyes of doubtful 

 function. If we confine the examination to the five species 

 taken below 2000 fathoms, we have one with well-developed 

 black eyes, two with abnormally small black eyes, one with 

 light-coloured eyes, and one with eyes of doubtful function. 



