BALANUS. 19 



end of the series of varieties, with their ribbed walls, very oblique radii, and coarsely 

 striated scuta, are extremely unlike B. amphitrite. 



With respect to the nomenclature of the present species, I have little doubt that I 

 have properly identified the Italian fossil specimens with B. concavus of Bronn, who has 

 given a very good figure of this species in his ' Lethaea Geognostica;' but it must 

 be confessed that the longitudinal striae on the scuta are not there represented. Consi- 

 dering the large size and frequency of this species in Europe and in the United States, it 

 has probably received several other names besides the two synonyms, quoted at 

 the head of this description. I should add that the true B. cylindraceus (not var. c) of 

 Lamarck, according to the plate given by Chenu in his ' Illust. Conch.' is the B. psittacus 

 of South America. I have seen in collections specimens of B. concavus labelled as 

 B. tulipa of Poli [B. tulipiformis of my Monograph), — a very natural mistake, without 

 the opercular valves be carefully examined. 



General Appearance. — Shell conical (fig. 4a), often steeply conical (fig. 4c), but 

 sometimes depressed and smooth (fig. 4d) ; orifice generally rather small, varying from 

 rhomboidal to trigonal, with the radii narrow, and generally in the fossil specimens very 

 oblique ; surface generally smooth, sometimes rugged, and in the Coralline Crag specimens 

 commonly ribbed longitudinally, the ribs being narrow. In the recent specimens the colour 

 is various, either dull reddish-purple with narrow nearly white, or wider dark longitudinal 

 bands ; or, again, pale rosy-pink with broad white bands ; or lastly, wholly white. The 

 radii are either darker or paler than the parietes. The opercular valves are either dark 

 purple or nearly white. Pale pink and white stripes are visible on some of the Italian and 

 Portuguese tertiary specimens ; and in most of the fossils the sheath is tinged dull red. 



Dimensions. — The largest actually recent specimen which I have seen, from the 

 Philippine Archipelago, had a basal diameter of 1*2 of an inch; the Peruvian pleistocene 

 specimen is 1*7 in diameter; specimens from the crag and from the Italian deposits, how. 

 ever, sometimes slightly exceed two inches in basal diameter, and three in height. 



Scuta : these in young and moderately-sized specimens are striated longitudinally 

 (fig. 4/), sometimes faintly, but generally plainly, causing the lines of growth to be beaded ; 

 but in large and half-grown specimens, the lines of growth are often extremely prominent, 

 and being intersected by the radiating striae, are converted into little teeth or denticuli. As 

 the striae often run in pairs, the little teeth frequently stand in pairs, or broader teeth have 

 a little notch on their summits, bearing a minute tuft of spines. In very old and large 

 specimens, the prominent lines of growth are generally simply intersected by deep and narrow 

 radiating striae (tab. I, fig. 4p). In one case, a single zone of growth in one valve was quite 

 smooth, whilst the zones above and below were denticulated. The valve varies in thickness, 

 which I think influences the prominence of the lines of growth and the depth of the strias. 

 These striae often affect the internal surface (fig. 4/t) of the basal margin, making it bluntly 

 toothed. The articular ridge (fig. 4n), is rather small, and moderately reflexed. The adductor 

 ridge (as already stated) varies remarkably ; in most of the recent Panama specimens (fig. 4#), 



