(sect, a), balanus tintinnabulum. 203 



although I have not seen this in any other variety, yet in Bal. concavus 

 a closely analogous plate, situated in the lateral depressor cavity, is 

 highly variable, and I am not willing to found a new species on one 

 minute point of structure, — a structure which is variable in another 

 species of the same genus. 



I have seen some cylindrical and conical specimens of B. tintinna- 

 bulum, from the coast of Mexico and California, only noticeable, as far 

 as the shell was concerned, from being rugged, and of a dull blueish- 

 purple ; but which had opercular valves exactly like those of var. 

 coccopoma, and therefore, as far as the scutum is concerned, approaching 

 closely in structure to var. concinnus, — all three from the west coast of 

 America. Hence I was at one time led to believe that there existed a 

 species on this line of coast, which represented B. tintinnabulum, and 

 which varied in external shape and colour in an analogous manner to 

 that species. But as the opercular valves in var. coccopoma are some- 

 times identical with those of var. communis, and as this is always the 

 case with the tergum of var. concinnus, and as the shell itself presents 

 no differences, it is scarcely possible to admit the existence on the 

 west coast of America of this supposed representative of B. ti?itin- 

 nabulum. 



With respect to var. intermedins I have little to say in addition to 

 the character given above : I have seen only two groups of specimens 

 in Mr. Cuming's collection : the chief interest in this variety is that it 

 shows that the next form must be ranked as a variety, and not as a 

 distinct species. 



Of var. occator (PI. 1, fig. k) I have seen several specimens, mostly 

 taken off the bottoms of vessels, and one specimen, marked in Mr. 

 Cuming's collection " South Seas." After having carefully examined 

 these specimens, I came to the conclusion, that the slightly oblique 

 radii — the general colouring, and more especially that of the sheath — 

 the scuta (PI. 2, fig. 1 b), with their sharp hood-like points, in 

 radiating lines — and the terga, with the spur so near to the basi-scutal 

 angle, were amply sufficient to distinguish it as a good species. Sub- 

 sequently, however, I found that the scuta in var. crispatns presented, 

 both externally and internally, exactly the same peculiar appearance. 

 In var. intermedins, I found the summits of the radii equally oblique, 

 and the general colouring nearly the same, and more especially a close 

 approach to the singular circumstance of the sheath differing in colour 

 towards the opposite ends of the shell. So that the position of the 

 spur of the tergum was the chief remaining character; and this 

 evidently varied considerably in the four or five specimens examined 

 by me, being either its own width, or much less than its own width, 

 from the basi-scutal angle : the outline, also, of the small portion of 

 basal margin, between the spur and the basi-scutal angle, likewise 

 varied much, being either angularly indented, or gradually curved 

 down towards the spur : so also the tip of the spur varied in shape. 

 The longitudinal furrow is unusually apt, in this variety, to remain 

 open. We know that the position of the spur varies considerably in 

 var. communis. Hence, although the spur, on an average, lies closer 

 to the basi-scutal angle in this than in any other variety, even than in 



