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the fusion is incomplete. To these last-mentioned characters, how- 

 ever, Howe does not attach so much importance, as there often 

 is some variation. 



Having now examined my material, I agree with Howe in 

 considering H. discoidea as a species separate from H. Tuna and 

 of the points named by Howe I think that the largeness and the 

 form of the utricles of the subcortical layer especially give good 

 characters. As to those of the peripheral utricles they may be 

 used with a little more care. Of both forms I have found typical 

 specimens, of H. Tuna very like fig. 1, Pl. I in Mrs. Gepp's mono- 

 graph and of H. discoidea quite agreeing with the figure (Plate 26) 

 of Howe and in these specimens the peripheral utricles were also 

 quite in accordance with Howe's description. Only I would point 

 out that I do not think that so very much stress can be laid on 

 the more or less contact above of the peripheral utricles with the 

 neighbouring cells, I have here found considerably variation; in 

 a specimen from the Mediterranean, collected by Dr. Ko Id er up 

 Rosenvinge at Antibes, even the cells were connected up half 

 their length. As to the fusion of the cells, on the other hand, I 

 have found in agreement with Howe that fusion is very rare in 

 H. Tuna var. typica but occurs often in H. discoidea var. typica. 



Things are quite different in the broad-jointed form of both 

 species found in deep water. Here fusion of the peripheral utricles 

 is almost quite common in both forms and as the external appea- 

 rance of the two forms is so very much alike also, I to begin with 

 was most inclined to consider them as belonging together. But after 

 a more thorough examination I have found that not only the form 

 and largeness of the utricles of the subcordical layer seem to be 

 very constant in each species, in agreement with the var. typica of 

 both, but the peripheral utricles also show some characters which 

 are rather constant. Thus the peripheral utricles seen from the 

 surface are, though little, nevertheless rather clearly smaller in 

 H. Tuna var. platydisca (Decne) Gepp 1 ) than in the broad form 

 of H. discoidea to which I propose the name var. platyloba (see 

 later), and the utricles are more easily separable in H. Tuna. 

 Howe for the rest has also pointed out that the forma platydisca 

 of Tuna shows occasional fusion. 



x ) Mrs. Gepp has examined the original specimen preserved in the Paris 

 Museum and found that the internal characters agree with those of 

 H. Tuna. 



