Dr. F. Miiller on Balanus armatus, 397 



hundreds upon hundreds of different forms to exhaust the va- 

 rieties of these Balani seated upon Carijoa ; nevertheless in 

 these, and likewise in the shells seated upon rocks, a steeply 

 conical form predominates. The two shells observed upon 

 Purpura were flatter than usual ; their walls were less steep, 

 and their base larger in proportion to the orifice. 



The surface of the walls is usually smooth, rarely furnished 

 with inconsiderable longitudinal ribs ; the shells attached to 

 rocks generally have stronger ribs. The colour of the walls 

 is sometimes quite pale ; sometimes they are striped with a 

 lighter or darker dingy brownish purple. The radii usually 

 exhibit a more or less distinct dingy purple colour. Not un- 

 frequently there is a remarkable difference of colour between 

 the two sides of the same shell ; and if we may imagine that 

 the influence of light has something to do with this, this ex- 

 planation is not applicable to a group of three shells of which 

 the lowest and largest is unusually dark-coloured, the second, 

 sitting upon this, is almost white, and the third and youngest, 

 which adheres to the second, has particularly distinct whitish 

 ribs, and between these pale-brown streaks. The sheath is 

 pale ; the opercular pieces partly pale, partly dark, but usually 

 reddish, at least towards the apex 



I never found the epidermis pi 

 rarely in traces upon the lower part of the walls ; but I possess 

 an example from a Reniera the walls of which are still com- 

 pletely covered with a yellowish membrane, and the radii of 

 which are, moreover, distinguished by their white colour. 



But, different as the shells of Balanus armatus may be in 

 their form and colouring, they all agree completely in the pe- 

 culiar form of the mouth, which reminds one of that of B. tri- 

 gonuSj though, unlike that of the latter species, it is always dis- 

 tinctly toothed *. The radii are always oblique, especially those 

 of the rostrum ; their free margins usually form with the wall of 

 the rostrum an angle a little under, and with that of the lateral 

 piece a little over 60°, meeting the alse of the lateral piece 

 about in the middle. In like manner the margins of the radii 

 of the lateral piece and of the alaj of the carino-lateral piece 

 meet each other about in the middle, whilst the margins of the 

 ala3 of the carina only meet the radii of the carino-lateral pieces 

 close to the walls of the latter. Like the denticulation of the 

 orifice, we find, as a second peculiarity in all well-preserved 

 shells, that the rostrum is a little bent inwards at the orifice. 



* The sole exception (and this is probably only apparent) is furnished 

 by the three shells which I foimd thrown up on the shore. Their mouths 

 are entire and toothless ; but I believe that they only lost their teeth 

 during' their rolling in the sea and surf. 



