(SECT. F), BALANUS UNGUUfORMIS. 297 



This species, the most ancient one as yet well known 

 in the genus, presents to the systematist a most un- 

 fortunate peculiarity, in the parietes being almost as 

 often as not permeated by small pores : I have seen no 

 other instance, except to a limited degree in B. glandula, 

 of this character being variable, and hence it must be still 

 considered of high classificatory value, in so varying genus 

 as Balanus. Owing to this varying condition of the 

 parietes, together with the basis being quite solid, our 

 present species has as good a claim to be ranked in the last 

 as in the present section ; indeed, I think it has more 

 affinity to B. crenatus and glandula in the last section, than 

 to any other recent forms : I have placed it in its present 

 place, owing to its intimate affinity to B. varians, in which 

 the parietes seem always to be solid ; and partly, I believe, 

 because all the first specimens examined by me exhibited 

 no traces of parietal pores. Owing to the kindness of 

 Mr. F. Edwards, I have seen the original specimens, excel- 

 lently figured by Mr. J. de C. Sowerby in the 'Mineral 

 Conchology 1 I can perceive no difference between B. un- 

 guiformis and erisma, excepting that the walls in the latter 

 are longitudinally folded, — a character we know to be vari- 

 able in so many species. In both varietes, the parietes are 

 sometimes porose and sometimes solid. The smaller speci- 

 mens, however, figured in the ' Mineral Conchology' to the 

 right hand, may possibly be a distinct species, as I infer 

 from the narrowness of their radii. 



General Appearance. — Shell, tubulo-conical, sometimes considerably- 

 elongated and sub-cylindrical : surface either very smooth, or slightly 

 folded, or deeply folded so as be strongly ribbed longitudinally: orifice 

 rather large, rhomboidal, narrow at the carinal end, toothed, but not 

 deeply : walls rather thin and fragile,: radii of moderate width, with 

 their summits oblique, not quite smooth. Basal diameter of largest 

 specimen, about three quarters of an inch. 



Scuta, with the external surface smooth : there is a trace of a furrow 

 running down the valve from the apex, near to the occludent mar- 

 gin, and this is only worth mentioning from the analogous furrows in 

 B. bisulcatus. Internally, the upper surface of the valve is roughened: 

 the articular ridge is very prominent, and slightly reflexed : there is no 

 distinct adductor ridge ; there is a slight but variable depression for 

 the lateral depressor. Tergum, with the longitudinal furrow shallow ; 

 spur moderately long, about one fourth or one fifth of the width of the 



