268 BALANID.E. 



the basis is ever calcareous. I have little doubt, also, that 

 this is the B. vulgaris of Da Costa. The B. balanoides, in 

 its corroded and therefore punctured state, is certainly the 

 B. punctatus of most British collections ; but I do not be- 

 lieve it is the B. punctatus of Montagu, which I have 

 scarcely any doubt is the CJithamalus stellatus, so often 

 found in the southern shores of England, and even in some 

 of the best arranged collections, mingled with our present 

 species. 



General Appearance. — The shell, in middle-sized and old specimens, 

 is almost invariably folded longitudinally and irregularly ; it is either 

 dirty white or very often pale brown, and punctured from the outer 

 lamina having been corroded, to which action it is extremely subject. 

 In very young specimens, the surface is usually quite white and smooth. 

 The shell is sometimes much depressed ; generally conical, but when 

 crowded together, cylindrical or club-shaped, one specimen being even 

 more than five-and-a-half times as long as wide. In Mr. Jeffreys' col- 

 lection there is a specimen 2*5 of an inch long, # 4;) in diameter at the 

 summit, only *2 in the middle, and rather more than *2 near the base. 

 Another specimen was 1*8 in length, its greatest diameter being *35 

 of an inch at the summit. On the other hand, I have seen a very 

 depressed variety, with deeply folded walls, in Mr. Thompson's collec- 

 tion from near Dublin, which was no less than four times as wide as 

 high ; so that the difference in proportion of height and greatest width, 

 in the two extreme specimens, was nearly as 10 to 1. Occasionally, 

 from some unknown cause, isolated specimens become cylindrical. The 

 orifice of the shell, in the much elongated specimens, is generally 

 deeply toothed. The radii are always narrow, sometimes extremely 

 narrow, and have their summits smooth and rounded. 



English specimens do not usually attain half an inch in basal 

 diameter ; I have, however, seen one from near Yarmouth *9 of an inch 

 in diameter. Specimens from Massachusetts seem rather larger than 

 the average size of British specimens, many being • 6 of an inch, and 

 one specimen a whole inch in basal diameter. 



The opercular valves so closely resemble those of B. crenatus, that 

 the description is necessarily comparative ; in some cases they could 

 hardly be discriminated ; generally, owing to the disintegration to which 

 this species is subject, the tips of the scuta are worn off, and hence the 

 articular ridges together form (PI. 7, fig. 2 a) a square projection, 

 indenting the two terga ; but I have examined young specimens and 

 others when not disintegrated, in which the opercular valves, viewed 

 externally, presented no difference whatever from those of B. crenatus. 

 The scuta, however, are, I think, generally rather thicker, with the 

 growth-ridges more prominent, and with t'.ie tips certainly less re- 

 flexed than is usual with B. crenatus. Internally, the articular ridge is 

 rather less prominent : there is no distinct adductor ridge. The tertja 

 are often rather narrower in proportion, and this especially holds good 



