262 BALANID.E. 



facts it will be seen in what confusion our commonest British 

 species of Balanus have been left. After due deliberation, 

 I have little doubt that this is the B. crenatus of Bruguiere, 

 and probably the B. rugosus of Montagu, but this latter 

 author omits all reference to the really important diagnostic 

 characters between this species and B. balanoides. The 

 B. crenatus is certainly the B. rugosus of Dr. Aug. Gould. 

 In various collections, I find specimens of B. crenatus, 

 when coming from the arctic regions, called B. glacialis, 

 arcticus, and borealis ; though I have not met with an 

 authentic specimen of the B. glacialis of Gray ('Supp. 

 Parry's Voyage/ 1819, p. ccxlvi), I have little doubt that 

 it would prove to be the present species. 



General Appearance. — White, usually of a dirty tint, from the yel- 

 lowish or brownish persistent epidermis: conical, generally (fig. 6a) 

 with the parietes rugged and irregularly folded longitudinally; but some- 

 times much depressed and extremely smooth (6 b) ; often cylindrical and 

 very rugged; occasionally club-shaped (6c), the upper part being much 

 wider than the lower : specimens in this latter condition sometimes 

 have extremely narrow parietes, like mere ribs, and wide radii. 

 The orifice in the cylindrical varieties is often most deeply toothed. 

 The radii are generally narrow, and have jagged oblique summits ; but 

 not infrequently they are so narrow as to form mere linear borders to 

 the compartments. The orifice is rhomboidal, passing into oval, 

 either very deeply or very slightly toothed. 



Ditne?isions. — The largest British specimen which I have seen was 

 only '55 of an inch in basal diameter : specimens from Greenland and 

 the northern United States frequently attain a diameter of three- 

 quarters of an inch, and I have seen one single somewhat distorted 

 specimen actually 1*6 of an inch in basal diameter. The specimens 

 from the glacial deposits of Uddevalla and Canada appear, on an 

 average, to attain as large or larger dimensions than those from the 

 United States : on the other hand, the specimens from the mammali- 

 ferous and Red Crag are smaller, the largest being only '35 in basal dia- 

 meter. When individuals have grown crowded together, their length 

 is often twice, and even occasionally thrice, as great as their greatest 

 diameter; thus I have seen a Greenland specimen 1*6 of an inch in 

 length, and only '75 in diameter. In the British Museum there are some 

 arctic specimens, one and a half inch in length, only half an inch in 

 diameter at the summit (fig. 6 c), thence tapering downwards to a 

 blunt point. 



Scuta ; the lines of growth are but little prominent: the surface is 

 generally covered by disintegrating membrane. The upper ends are 

 usually a little reflexed, so that the tips project freely as small flattened 

 points. Internally, the articular ridge is highly prominent and some- 

 what reflexed : there is no adductor ridge, but a very distinct impres- 

 sion for the adductor muscle : the depression for the lateral depressor 



