1890.] OF THE EYE IN ARCTURUS. 371 



narrow peripheral band left which is clear. The whole vitreous body 

 appears to be more or less granular and opaque. 



(5) Arcturus hrunneus, F. E. Beddard. 



In this species the vitreous bodies or lenses of the ommatidia have 

 the form which is illustrated in the drawing exhibited (Plate XXXI. 

 fig. 13) ; tlieir shape is usually that of a buffet with the convex 

 outer surface and a straightish margin where the lens comes into 

 actual or at any rate very near contact with the rhabdom. As a 

 rule the lens is decidedly smaller. 



The rhabdom, on the other hand, is particularly large. 



(6) Arcturus glacialis, F. E. Beddard. 



The eye of this species calls for no lengthy description, the vitreous 

 bodies have the same curious muffin-shape that they have in 

 A. spinosus ; the rhabdom is large, and the nuclei of the retiuula- 

 cells are placed below it. 



(7) Arcturus studeri, F. E. Beddard. 



This is the only shallow-water species besides A.furcatiis and 

 A. americanus that I have studied ; unfortunately in this case, as in 

 that of A. americanus, I am dependent upon a single sketch which I 

 made some years ago ; the preparations themselves are missing. This 

 is particularly to be regretted, as A. studeri resembles in some par- 

 ticulars species that only occur in deep water. The vitreous bodies, 

 however, are quite like those of A. furcatus in their perfect trans- 

 parency and in their general shape. I am unable to give any details 

 about the rhabdom ; it does not, however, seem to be particularly 

 large ; the retinula-cells are unlike those of A. furcatus, and like 

 those of A. spinosus and all the deep-sea species described in the 

 present paper in that their nuclei are placed below the posterior ex- 

 tremity of the rhabdom. Whether there is much or little pigment 

 I cannot say. 



The following table indicates the depths at which the various 

 species described in the present paper were met with : — 



1. Arcturus furcatus. 7-127 fathoms (one specimen in 1675 



fathoms). 



2. Arcturus americanus. .55 fathoms. 



3. Arcturus studeri. 25-127 fathoms. 



4. Arcturus glacialis. 1675 fathoms. 



5. Arcturus brunneus. 1600 fathoms. 



6. Arcturus anna. 600 fathoms. 



7. Arcturus cornutus. 500 fathoms. 



8. Arcturus spinosus. 1375 fathoms. 



The first three species are therefore to be looked upon as shallow- 

 water forms ; the remainder as true deep-sea species. 



