404 Dr. F. Miiller on Balanus armatus. 



Ova. — 0'17 millim. long, 0'09 millim. thick. In the larvce, 

 I find nothing remarkable ; they are very like those of Tetra- 

 clita jwrosa. 



Affinities. — The nearest ally of Balanus armatus is B. tri- 

 gonus. Indeed, whether the former might not better be regarded 

 as a mere variet}^, and indicated as B. trigonus, var. armatus, 

 can only be decided by comparison with numerous examples 

 of B. trigonus from various localities. But it may be cited, in 

 favour of its specific title, that B. trigonus has hitherto been 

 found only in the Indian and Pacific Oceans, and not in the 

 Atlantic, and only on the shells of mollusca and on wood, but 

 not in sponges — that in B. trigonus the shell is usually shal- 

 low and ribbed, and the mouth has entire margins and is 

 almost equal-sided, whilst in B. armatus the shell is usually 

 abruptly conical and smooth, and the mouth always distinctly 

 toothed and pentagonal — that the scuta are narrower in B. ar- 

 matus — and that the armature of the third pair of feet, which 

 was never missed in B. armatus, and indeed caught the eye at 

 the first glance, is not mentioned by Darwin in B. trigonus, 

 any more than the strong tooth on the peduncle of the fifth 

 pair, which is always present in B. armatus. 



The shells seated upon Carijoa, when predominantly deve- 

 loped in length, and especially when the base somewhat pro- 

 jects, sometimes resemble in general appearance the species 

 living on Gorgonige, which, in Darwin's work, form the sec- 

 tion B of the genus Balanus ; but this resemblance is merely 

 the consequence of the similar mode of adhesion, and scarcely 

 the sign of any near affinity. In other respects Darwin's re- 

 marks upon the affinities of B. trigonus apply to our species. 



Signijication of the armature of the cirri. — A similar arma- 

 ture of tlie cirri with spines and points, although not so strongly 

 developed, occurs in other Balani. In individual examples 

 of B. imjjrovistcSy var. assimilis, these spines, elsewhere di- 

 rected upwards, even occur directed downwards and backwards, 

 as in B. armatus, on the outside of the joints of the third and 

 fourth pairs of feet. This armature of spines and points occurs 

 almost exclusively on the surfaces turned towards the margin 

 of the opercular fissure, as on the outer surface of the middle 

 pairs and on the dorsal surface of the last pair. In this posi- 

 tion they cannot serve for the seizure of any prey, but scarcely 

 for any other purpose than the cleansing of the fissure. In 

 fact, in living animals, we see that the cirri of the third and 

 fourth pairs, the outer surface of which is particularly richly 

 spinous, are those which pass closely along the margin of the 

 opercular fissure during tlieir protrusion and retraction. 



Now, that it is exactly in spongicolar species, otherwise by 



