292 BALANIDiE. 



calcareous basis, that I should not be surprised if portions of a true 

 membranous basis did really in some cases exist. 



Mouth : labrum with the notch wide, generally with a few little 

 teeth ; mandibles with three teeth, and some inferior knobs : maxillae 

 notched. Cirri, first pair with one ramus shorter by three segments 

 than the other ramus. Second and third pairs short, of nearly equal 

 length, thickly clothed with spines; segments very little protuberant. 

 Posterior cirri, having elongated segments, supporting seven pairs of 

 spines. 



Far. sordidus. — This form is very common on the tidal shores of the 

 Strait of Magellan, and of the southernmost parts of Tierra del Fuego, 

 near Cape Horn : it lives attached to rocks, mytili, and logs of wood, 

 and is associated with Chtha mains scabrosus. It almost certainly is 

 the most antarctic form of the genus Balanus. If I were guided by 

 external appearance alone, I should certainly separate this form speci- 

 fically from B.Jlosculus, but, as will be seen in the following description, 

 the differences consist only in var. sordidus being much duller and 

 rather differently coloured, in the longitudinal folds being sharper and 

 more prominent, and in the whole shell being rather more globular, 

 and on an average rather larger; but in the true B. Jlosculus there is 

 considerable variation in all these respects, as there likewise is in 

 var. sordidus; thus some of the cvlindrical varieties of the latter 

 have less prominent ridges than even var. Jlosculus. In general ap- 

 pearance 1 have seen some nearly, but not exactly, intermediate 

 forms ; therefore, I do not feel positive that these forms may not be 

 specifically distinct, but have failed, after careful examination, to find 

 any sufficient diagnostic characters. Moreover, in the case of Balanus 

 Icevis, I was led to believe that there is an equal and somewhat 

 analogous amount of variation in the specimens inhabiting Tierra del 

 Fuego and northern Chile ; and in this case I was enabled to show the 

 existence of strictly intermediate forms in the intermediate districts. 



The shell in var. sordidus is generally globulo-conical, dirty white, 

 frequently with a green tinge, from the growth of confervoid matter. 

 Orifice small. The exterior surface is covered with numerous pro- 

 minent, narrow, sharp ribs or folds, the basal margin being serrated 

 with projecting points where the folds terminate. When the radii are 

 not developed, the sutures are very often obscure. Internally, the shell 

 is faintly tinted of a port-wine purple. In all points of structure this 

 form is identical with the true B.Jlosculus. In some few specimens 

 the whole exterior surface was disintegrated and smooth ; and this is 

 generally the case with the upper parts of the shell. Some other 

 specimens, which had grown crowded together on wood, had become 

 cylindrical, and consequently the orifice was as large in diameter as 

 the shell, namelv, half an inch : in some of these cvlindrical varieties 

 the sheath was entirely soldered to the walls. The largest specimens 

 which I have seen were *6 of an inch in diameter; and above one inch 

 in height. 



Affinities. — This species, in its opercular valves, even in such trifling 

 characters as the strength of the opercular membrane, and in its cirri, 

 approaches closely to B. cariosus. We even see on the under side of 



