488 balanid^e. 



larly in size, to mere beads, at the extreme basal edge, and are arranged 

 symmetrically. The general aspect of the shell depends chiefly on 

 the degree to which the surface has been disintegrated, and differs 

 greatly in the two extreme states. When well preserved, the general 

 appearance is very elegant ; the scales are all neatly imbricated ; they 

 terminate upwards in points, but with their extreme tips generally 

 broken ; from laterally overlapping each other, their external surfaces 

 (as seen, when corrroded, in fig. 4 d, or when slightly exposed after the 

 continued growth of their basal margins, in fig. 4 a) become longi- 

 tudinally keeled, often with a secondary ridge or shoulder on one side ; 

 they are, also, crossed by rather conspicuous and regular lines of 

 growth, or more strictly, former lines of union between the several 

 valves : the orifice of the shell in this perfect condition is sub- 

 rhomboidal and notched, and the scuta are united to the terga by 

 nearly straight sutures. On the other hand, when the shell has been 

 considerably corroded, and this seems to be the more common con- 

 dition, the appearance is not elegant : the scales in the successive 

 whorls are not imbricated, but owing to their upper parts having 

 been worn down, they present a tesselated surface (4 cl), with the 

 tesserse graduated in size, and of a peculiar shape, namely, a rectangle, 

 with a more or less broad square projection on the exterior side, toge- 

 ther often with a large square notch on one or both corners, caused 

 by their laterally overlapping each other. Some of the shells are so 

 deeply corroded, that no portion of the original surface is preserved, 

 excepting the lowermost bead-like scales ; and the whole shell has so 

 rugged an aspect, that the successive whorls of the worn-down valves 

 might easily be overlooked. In the corroded specimens, the orifice 

 approaches to circular in outline, and is large and nearly entire : the 

 scuta and terga are deeply interlocked together. The largest specimen 

 which I have seen was one inch and a quarter in basal diameter. 



Structure of the Shell. — The eight inner normal compartments are 

 not thicker than the outer valves, and are far thinner than in ordinary 

 sessile cirripedes. They are arranged as in Octomeris. The lateral 

 compartments are broader than the rostro-lateral and carino-lateral com- 

 partments. The shelly laminse, of which these compartments and the 

 opercular valves are composed, alternate with yellow membranous layers, 

 exactly as is the case with Octomeris. The lateral edges of the com- 

 partments, beneath the alee, in the six compartments having alee, bend 

 inwards, especially just above the basis, so that the compartments in 

 their lower parts (fig. 4 c) stand much more separate than is usual. 

 The basal edge of each is irregularly toothed. The sheath presents no 

 particular character. The eight compartments have longitudinal shoul- 

 ders and ribs on their external surfaces, caused by the lateral overlap- 

 ping and pressure of the exterior scales. They are also marked by slight, 

 transverse or oblique calcareous ridges, caused by the attachment of the 

 membrane, by which they are united to the smaller compartments or 

 scales outside them. A new line of attachment, and consequently a new 

 ridge is formed, lower and lower down at each period of growth, as the 

 shell is added to at the basis, — in the same manner as new r ridges are 

 added to the lower edge of the sheath at each period of growth. The 



