BALANUS. 23 



6. Balanus crenatus. Tab. I, fig. 6a — 6g. 



B. crenatus. Bruguiire. Encyclop. Method, (des Vers) 1789. 



Lepas foliacea, var. a. Spengler. Skrifter af Naturhist. Selskabet, b. i, 1790. 



— borealis. Donovan. British Shells, PI. 163, (1802-1804). 

 B. rugosus. Pulteney (?) Catalogue of Shells of Dorsetshire, 1799. 



— Montagu (?) Test. Brit., 1803. 



— Gould (!) Report on Invertebrata of Massachussetts (1841), fig. 10. 

 B. glacialis (?) J. E. Gray. Suppl. Parry's Voyage, 1819. 



B. elongatus (!) clavatus (!), auctorum variorum. 



B. parietibus, sed non basi ports perforatis ; testa alba ; radiorum marginibus superi- 

 oribus obliquis, asperis, rectis ; scuto sine adductoris crista ; tergi calcare rotundato. 



Parietes bat not basis permeated by pores ; shell white ; radii with their oblique 

 summits rough and straight; scutum without an adductor ridge; tergum with the spur 

 rounded. 



Fossil in glacial deposits of Scandinavia and Canada, Mus. Lyell ; in the mammaliferous and Red 

 (Sutton) and Coralline Crags ; Mas. S. Wood, J. de C. Sowerby, Bowerbank, &c. Miocene formation, 

 Germany, Mus. Krantz. 



Recent in Great Britain, Scandinavia, Arctic Regions as far as Lancaster Sound, in 74° 48' N. ; 

 Behring's Straits ; United States ; Mediterranean ; West Indies ; Cape of Good Hope. Generally attached 

 to shells and Crustacea in deep water. 



Under the last species I have shown that the porose parietes, but solid basis, distin- 

 guish this species easily from all the others, with the exception of B. porcatus, from 

 which it can readily be known by the characters of its opercular valves, as already there- 

 under stated. Judging by external appearances alone, which ought never to be trusted to 

 in the identification of any sessile cirripede, this species might easily be confounded with 

 Bal. dolosus, found fossil in the same deposits. 



This species presents a great diversity of external aspect : I have had figured (Tab. I, 

 fig. 6a) one of the commonest appearances presented by it ; but frequently the shell is 

 quite smooth and -depressed, or extremely much elongated and cylindrical, or even club- 

 shaped. The basis is generally thin and slightly furrowed in lines radiating from the 

 centre, but it is not permeated by pores ; when, however, in large and old specimens it 

 becomes thicker, as in Tab. I, fig. 6c, its edge is very distinctly pitted by little hollows, 

 which might sometimes be easily mistaken for the orifices of pores : the absence of pores 

 is a very important character in the diagnosis of B. crenatus. The basis is less firmly 

 attached to the supporting surface than is usual with most cirripedes, and consequently it 

 often separates from it together with the parietes. With regard to the opercular valves 

 {6d — 6g) drawn from recent specimens, I need here only state that the most conspicuous 



