442 BALAN1D.E. 



peduncle is attached with remarkable strength to these rib-like zones 

 of the sheath. The alse (a in fig. 4 b) are represented by mere angular 

 shoulders, received into very slight notches, and placed at the inner 

 ends or entrances of the double walls, or rays as I have called them. 

 With respect to the radii, they also are in an extremely rudimentary 

 condition ; but a thin layer of shell, apparently continuous and homo- 

 logous with the sheath, extends from the sheath along both sides of 

 each ray, and on the rostral side (whence the radius ought to arise), 

 about half-way from the end of the ray, gives rise to a projection or 

 ridge (d, in fig. 4 b) which runs from the top to the base of the shallow 

 shell. From this longitudinal ridge, septa, parallel to the basis, extend 

 to nearly the extremity of the ray or double wall. These represent 

 the radii; but they never grow, so as to increase the diameter of the 

 shell. These radii evidently correspond to the additional or pseudo- 

 radii in Coronula, which in that genus lie between the parallel, as here, 

 and folded parietes. Of the true radius, having the same thickness as 

 the paries, I here saw only traces in an internal, very slight, longi- 

 tudinal ridge running up the shell, close to the outer extremity of each 

 ray or double wall. 



The membranous Basis is united all round to a rather wide flap of 

 membrane which is inflected from the outer surface of the shell. The 

 cement-glands appear to be mere enlargements of the cement-trunks, 

 which latter extend in two nearly straight and parallel lines. From 

 each gland two cement-ducts proceed, one of which runs parallel to 

 the cement-trunk. 



The pseudo-peduncle, forming the main part of the animal, has, as 

 far as external appearance is concerned, been sufficiently described. The 

 part forming the hood apparently answers to the protuberant lips of the 

 operculum, and the lower part to the sub-cylindrical shell of Tubicinella ; 

 both shell and peduncle in the two genera being wider at top than at 

 bottom. If in imagination we chip away (an action always in progress) 

 the whole upper part of the shell of Tubicinella, leaving only two or three 

 zones of growth at the base, we shall convert it into a Xenobalanus, 

 with every internal part and organ occupying the same relative posi- 

 tion : for it should be borne in mind that the shell of Tubicinella is 

 lined close down to the basis by the opercular membrane, and this is 

 strictly comparable with the outer membrane of the pseudo-peduncle 

 of Xenobalanus. The body, as in Tubicinella, is attached in a vertical 

 position, with the longer axis of the thorax and of the much elongated 

 prosoma extending in the direction of the longitudinal axis of the 

 pseudo-peduncle. The point of attachment of the body to the lower 

 part of the hood is much elongated, but presents the usual muscles 

 running to near the base of the labrum and embracing the prosoma. 

 The adductor scutorum muscle is well developed, and is placed close 

 beneath the mouth, where the collar or hood commences folding over: 

 hence, no doubt, the lower end of the large and long orifice into the 

 sack can be closed by the adductor ; but the upper end probably can 

 only be blocked up by the outer surfaces of the curled cirri. The 

 scuta, I may add, if such had existed, would certainly have covered the 

 point where the adductor muscle is attached to the exterior membrane. 



