386 BALANID.E. 



ing ofi' on both sides little septa, often sub-branched ; it is 

 of nearly uniform width; and there is no distinct inner lamina. 

 The outer portion (b), which often equals or exceeds in 

 thickness the inner portion, is, in fact, the normal outer 

 lamina, developed to an unparalleled degree. In most 

 Cirripedes the edge of the radius is received in a slight 

 furrow in the opposed compartment, the lid of which furrow 

 is narrow, and matches the outer lamina of the radius ; 

 here the lid of the recipient furrow is very broad, and 

 resembles the outer lamina of the radius in all its characters. 

 In order to allow of growth between the thick opposed 

 edges of the outer lamina of the radius and the lid of the 

 recipient furrow, the two surfaces are finely dentated (look 

 in tig. 5, under the pits, marked b), almost like the crown 

 of a molar tooth ; thus allowing films of corium to enter. 

 The structure here described is common, in a greater or less 

 degree, to all three species, but is best seen in C. testicdi- 

 naria. In this species, moreover, (fig. 5, b), the outer 

 lamina, instead of being smooth and of either equal or 

 gradually increasing thickness from top to bottom, is gene- 

 rally, but not always, (fig. 1 a), deeply pitted or notched 

 in transverse lines, the outer lamina being thus rendered 

 alternately thicker and thinner, and so formed into 

 transverse ridges and valleys. Hence the lines of suture 

 become toothed, the points of the teeth facing each other, 

 and not interlocking. In the transverse section, fig. 1, 

 PL 15, of the same species, taken high up across the shell, 

 (/) is the pitted outer lamina, and (e) the inner portion of 

 the radius. Although the radii are thus specially added to 

 in thickness, they are not so thick as the very thick walls, 

 and hence the lines of suture form furrows more or less 

 deep. The alee are of moderate thickness, and have their 

 sutural edges crenated by fine transverse septa. 



Rostrum. — I have already alluded to the peculiar com- 

 pounded structure of this compartment, unlike anything 

 we have as yet seen."* The thin outer lamina is quite 

 continuous, and shows no trace of the triple nature of the 

 compartment; as may be seen by comparing the drawing 



* My attention was first called to this peculiar structure of the rostrum by 

 Mr. Stutcbbury. 



