30 FOSSIL CIRRIPEDIA. 



Parietes thin, sometimes permeated by pores ; radii without pores, with their upper 

 margins oblique ; sutural edges very finely crenated ; basis without pores. Tergum with 

 the spur narrow, bluntly pointed. 



Var. erisma (fig. 4>b), with the walls longitudinally folded or ribbed. 



Fossil in the Eocene formations, Isle of Wight, Colwell Bay ; Hordwell ; Barton, (Chama Bed) ; Headon ; 

 Bembridge ; Bergh, near Klein Spauwen, Belgium (?). Attached to various shells and wood. Mus J. de 

 C. Sowerby, E. Forbes, F. Edwards, Charlsworth, T. Wright, Bowerbank, Tennant, Bosquet. 



This species, the most ancient one as yet well known in the genus, presents to the 

 systematist a most unfortunate 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 the 

 recent B.glandula, of this character being variable, and hence it must be sti]J considered 

 of high classificatory value, in so varying a genus as Balanus. Owing to the kindness of 

 Mr. F. Edwards, I have seen the original specimens, excellently figured by Mr. J. de C. 

 Sowerby, in the ' Mineral Conchology,' under the names of B. unguiformis and erisma, 

 between which I can perceive no difference, excepting that the walls in the latter are 

 longitudinally folded, — a character we know to be variable in many species. In both 

 varieties, the parietes are sometimes porose and sometimes solid. The smaller specimens, 

 however, figured in the ' Mineral Conchology' to the right hand of the Plate, may possibly 

 be a distinct species, as I infer from the narrowness of their radii. This species is inti- 

 mately allied to B. varians, a fossil from the ancient tertiary plains of Patagonia. It is also 

 allied to the recent B. crenatus and glandula. 



General appearance. — Shell (fig. 4a), tubulo-conical, sometimes even 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 (fig. 4c), with the external surface smooth : there is a trace of a furrow running" 

 down the valve from the apex, near to the occludent margin, and this is only worth 

 mentioning from the analogous furrows in B. bisculatus. Internally (fig. 4e), 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 (fig. 4d), with the longitudinal furrow shallow; spur 

 moderately long, about one fourth or one fifth of the width of the valve ; placed at about 

 its own width from the basi-scutal angle; basal end bluntly pointed ; the basal margin on 

 the opposite sides of the spur forms a nearly straight line ; the carinal margin has an 

 extremely narrow border formed by upturned lines of growth. Internally (fig. 4/), the 

 surface is roughened with little points : the articular ridge is prominent : the crests for the 

 tergal depressores moderately prominent. 



