[56 THE VOYAGE OF II. M.S. CHALLENGER. 



ing them as representatives of a new section of the genus Balanus. The absence of radii. 

 the solidity of the parietes, the membranous base, form the characteristic marks of this 

 section, which at present comprises only two species. Both species are from rather 

 dee]) water; and we need hardly doubt that the structure of the shell affords a 

 very striking instance of the influence of their living at a more considerable depth. 

 Beinu' solid (not permeated by pores), the compartments have by no means the strength 

 of other species of the genus, which, as a rule, have the compartments composed of two 

 laminae united by longitudinal septa ; and, moreover, the strength is diminished by 

 the absence of the radii, which in other species, as modified parts of the side of the 

 compartments, overlap the adjoining compartments. In the present species the compart- 

 ments adhere so feebly as almost to separate on being manipulated. The largest speci- 

 men of Bala nus corolliformis which was obtained, and which, therefore, has been figured 

 (PI. VI. figs. 21, 22), showed the compartments quite loose from one another, and only 

 adhering by means of the muscles which were attached to them. For an animal living- 

 near the surface, the violent beating of the waves would soon prove fatal if its walls 

 showed the structure of our Balanus corolliformis. It was taken at a depth of 150 

 fathoms, at which depth it may be taken for granted that the water does not 

 experience the direct influence of the beating of the waves. The other species was taken 

 at a depth of no less than 516 fathoms. 



Balanus corolliformis has to a certain degree the shape of the corolla of a flower, the 

 orifice of the shell being much wider than its base, and being very deeply toothed. The 

 latter character is due to the obliquity of the summits of the alse, and to some extent 

 also to the circumstance that the alas are very broad at a certain distance from the base, 

 and then slope downwards, so as to be extremely narrow at the base of the shell. In the 

 largest specimen of this species which was collected, the width of the shell, which is very 

 considerable at the orifice, grows smaller downward, but remains the same almost from 

 the middle to the base. The growth-ridges run regularly nearly parallel in the upper 

 half of the shell, and much more irregularly in the under half. As in some of the cases 

 in which the radii are not developed, mentioned by Darwin, the sutures of the valves in 

 the lower half of the shell at least are marked only by fissure-like lines. The sheath 

 extends one-third down the shell ; the rostrum, which, seen from the exterior, does not 

 show a trace of radii, has, wheu seen from the interior, the sheath divided into three 

 parts, of which the two lateral portions may be considered as rudimentary radii. The ros- 

 trolateral compartment and the extremely narrow carino-lateral compartment show also on 

 the inner side traces of what might be considered a radius. 



Colour of the shell dirty white ; the limits of the growth-ridges are coloured yellowish 

 by the persistence of the membrane, which is distinctly hairy. The hairs are short, stiff, 

 chitinous spines. At different places the surface is irregularly invested by calcareous 

 masses of a Polyzoon. Of the smaller specimens some are attached to the spines of an 



