402 BALANIDiE. 



a shell of C. balamaris ; to perceive the full amount of com- 

 plication, it is advisable to trace the wall of any one of the 

 compartments, from one suture (s) to another. In this 

 figure the sutures are purposely drawn a little open. It 

 may be seen that the new transverse loops, and conse- 

 quently the new folds of the walls, have been, in this species, 

 mostly formed in symmetrical order, on both sides of the 

 six sutures ; this results from the transverse loops on the 

 sutures almost always giving rise contemporaneously to 

 three new transverse loops. In C. diadema the transverse 

 loops on the sutures usually divide into only two new loops, 

 one on the rostral side and one still remaining at the 

 suture ; hence the folding of the walls in this species is 

 much less symmetrical. The number, however, of the 

 transverse loops and the exact pattern of the folding is 

 variable in all four species of the genus. I may further 

 add, to show the complication of the folds, that in a shell of 

 C. balamaris, having a basal diameter of two inches, and 

 which had the walls as little folded as ever they are, yet 

 I found, by careful measurement, that the entire basal 

 edge of the wall, if stretched straight, would have extended 

 for a length of fifty-two inches ! Therefore, if the wall had 

 not been folded, but had been simply circular, as in ordinary 

 cirripedes, the basal diameter of the specimen would have 

 been between sixteen and seventeen inches ! 



The central membranous basis is flat, but the bottom of 

 the folded walls of the shell is concave, which is caused by 

 the outer ends of the folded walls having grown at a greater 

 rate than the inner ends. The concavity is deep in C. 

 diadema ; in C. balanaris it is much less so, and here the 

 inner hood-like ends of the folded walls are rather abruptly, 

 but in a variable degree, produced downwards, generally 

 even slightly beneath the level of the circumference of the 

 shell; this fact is of interest in relation to the peculiar, 

 depending, spur-like processes in the genus Platylepas. A 

 lateral view of a compartment in both these species, is given 

 in PI. 10, figs. 2 and 3; and by supposing in each case 

 a compartment to stand opposite, at a distance which may 

 be judged of from fig. 5, the vertical sectional outline 

 of the whole shell will be understood : in fig. 3 of 



